Open-source alternatives to Pulsar

Hazelcast is a distributed data platform that combines an in-memory data grid with a stream processing engine to support real-time analytics and event-driven applications. It functions as a partitioned, distributed key-value store that replicates data across cluster nodes to provide low-latency access and high availability. The platform also serves as a distributed SQL query engine, allowing users to execute standard SQL statements against both in-memory datasets and external data sources. What distinguishes Hazelcast is its use of a distributed consensus subsystem to maintain strongly consis

FoundationDB is an ACID-compliant distributed transactional key-value store. It functions as a scalable database engine that ensures strict serializability and data consistency across a cluster of servers using a shared-nothing architecture. The system is distinguished by its multi-region replication capabilities, allowing data to be synchronized across different datacenters for high availability and disaster recovery. It utilizes optimistic concurrency control to manage distributed transactions and employs a majority-based coordination system to maintain cluster state. The platform provides

NATS Server is a high-performance, lightweight messaging system designed for cloud-native applications, edge computing, and distributed microservices. It functions as a distributed publish-subscribe broker that routes messages using hierarchical, dot-separated subject strings, enabling decoupled communication between services without requiring centralized broker lookups. The system supports core messaging patterns including asynchronous publish-subscribe, request-reply, and load-balanced queue processing. The platform distinguishes itself through a decentralized architecture that eliminates t

Redis is a high-performance in-memory key-value store that functions as a distributed cache, message broker, and NoSQL database. It provides sub-millisecond read and write access to data stored in RAM and can operate as a vector database for indexing high-dimensional embeddings. The system supports a wide range of data storage and synchronization primitives, including the management of strings, hashes, lists, sets, and JSON documents. It enables real-time data operations through atomic transactions, hybrid persistence using snapshots and append-only logs, and high-availability configurations

CubeFS is a distributed cloud storage system designed for managing file and object storage across datacenters and hybrid clouds. It functions as a multi-tenant distributed file system and object store capable of handling data at exabyte scale, utilizing a distributed architecture to store unstructured content. The system is distinguished by a multi-protocol interface layer that allows simultaneous data access through S3, POSIX, and HDFS interfaces. It employs a decoupled compute-storage architecture to scale processing and persistence independently and implements fine-grained isolation polici

Garnet is a multi-threaded in-memory database and distributed key-value store. It functions as a high-performance remote cache store that implements the RESP wire protocol to maintain compatibility with existing Redis clients and libraries. The project is distinguished by a shared-memory architecture that enables parallel request processing across multiple cores for sub-millisecond latency. It features a tiered storage system that automatically offloads colder data from system memory to SSD or cloud storage layers, and includes a specialized vector search database for high-dimensional similar

Pinot is a distributed, columnar analytical database designed for high-concurrency, low-latency query processing. It functions as a real-time OLAP datastore, enabling interactive, user-facing analytics by ingesting and querying massive datasets from both streaming and batch sources. The system architecture relies on a centralized controller for cluster coordination and a distributed segment-based storage model to ensure horizontal scalability. The platform distinguishes itself through a hybrid ingestion pipeline that unifies real-time event streams and historical batch data into a single quer

RocketMQ is a distributed messaging and streaming platform designed for building event-driven applications. It serves as middleware to decouple services using publish-subscribe and request-reply patterns, and functions as a transactional messaging system that ensures atomicity by linking message delivery to local transaction outcomes. The platform includes specialized capabilities as a Kubernetes-native message broker for container orchestration environments and an MQTT broker for ingesting event data from mobile applications and hardware terminals. The system covers high-throughput data str

QuestDB is a high-performance, distributed time-series database designed for the ingestion, storage, and analysis of massive datasets. It functions as a real-time analytics platform that utilizes a columnar storage engine to optimize disk input and output, enabling efficient analytical scans and complex windowing operations on streaming data. The platform distinguishes itself through specialized capabilities for handling asynchronous time-series streams, including advanced join algorithms that align disparate data sets based on precise timestamp lookups. It supports high-volume ingestion thro

Highly scalable realtime pub/sub and RPC framework

ioredis is a performance-focused Redis client for Node.js applications. It provides a comprehensive interface for interacting with Redis servers, including specialized clients for sharded clusters and Sentinel-based high availability environments. The project distinguishes itself through advanced networking and execution capabilities, such as automatic event-loop pipelining to reduce overhead and a system for routing read-write traffic between primary and replica nodes. It also features a dedicated Lua scripting interface that allows server-side scripts to be registered as custom client comma

graphql-engine is an automated GraphQL API engine that transforms database tables and relationships into a queryable GraphQL schema. It functions as a federation gateway and mapper, instantly generating APIs with built-in filtering, pagination, and mutations from existing databases and remote schemas. The project distinguishes itself through a fine-grained access control layer that enforces row-level and field-level permissions. It further provides a real-time data subscription server that converts standard queries into live streams and a system for triggering event-driven webhooks and notifi

Neon is a serverless PostgreSQL database platform designed with a decoupled storage and compute architecture. It functions as a multi-tenant system that isolates data and compute resources for independent users on shared cloud infrastructure, utilizing a specialized PostgreSQL storage engine. The platform features a database branching system that allows for the creation of isolated, instant copies of a database for testing and development. It further distinguishes itself with an HTTP-based SQL gateway, enabling the execution of queries via HTTP requests and JSON responses without the need for

Soketi is a high-performance WebSocket server and real-time event broker that implements the Pusher protocol. It functions as a multi-tenant WebSocket gateway, allowing multiple isolated applications to manage persistent client connections and broadcast events across public, private, and presence channels. The project is distinguished by its distributed architecture, using pub-sub state synchronization via Redis or NATS to scale horizontally across multiple server instances. It features symmetric payload encryption for private channels, ensuring the server acts as a relay without accessing pl

GreptimeDB is a distributed, open-source time-series database built for unified observability. It stores and queries metrics, logs, and traces together in a single columnar engine, supporting both SQL and PromQL for analysis. The database is designed as a Kubernetes-native operator with a decoupled compute and storage architecture, enabling horizontal scaling and multi-region deployment. What distinguishes GreptimeDB is its role as a multi-protocol ingestion gateway, accepting data through OpenTelemetry, Prometheus Remote Write, InfluxDB, Loki, Elasticsearch, Kafka, and MQTT protocols without

OceanBase is a distributed SQL database designed for high availability and strong consistency across multiple nodes and regions. It functions as a hybrid transactional and analytical processing engine, allowing real-time analytics and transactions to execute on a single data copy. The system also serves as a vector database engine for indexing and querying vector data to power semantic search and recommendation systems. The platform features native compatibility layers for MySQL and Oracle, enabling the migration of legacy workloads without rewriting SQL code. It utilizes a Paxos-based distri

YugabyteDB is a distributed SQL database and relational data store designed for horizontal scalability and high availability across multiple nodes or regions. It functions as a cloud-native system that ensures continuous availability and supports PostgreSQL compatible query languages and drivers. The system includes specialized capabilities as a vector database for AI, utilizing high-dimensional indexing to perform similarity searches. It is engineered as a multi-region cloud database that synchronizes data across different geographic locations to maintain global availability. The project co

This is a Golang client library for interacting with a cloud native distributed messaging system. It provides the necessary tools for Go applications to exchange messages using publish-subscribe and request-reply patterns, as well as specialized clients for managing persistent streams and distributed storage. The library includes a JetStream client for durable message streaming and replay, a Key-Value store client for managing distributed state with versioning and watchers, and an Object Store client for the storage and retrieval of large binary files via chunked delivery. The implementation

This project is a comprehensive Java backend engineering guide and technical reference focused on high-concurrency design, distributed systems, and microservices architecture. It provides detailed strategies for decomposing monolithic applications, managing service discovery, and implementing the architectural patterns required for scalable backend environments. The repository distinguishes itself through an extensive collection of big data algorithmic references and database scaling strategies. It covers memory-efficient techniques for analyzing massive datasets, such as Top-K element extrac

Sarama is an Apache Kafka Go client library that provides native support for the Kafka protocol. It includes a protocol client for managing offsets and timestamps, a producer implementation for sending messages, and a consumer group coordinator to balance workloads across multiple instances. The library enables high throughput data streaming through concurrent message production and maintains strict partition ordering during network retries. It supports secure communication with Kafka brokers using certificate-based encryption to protect data traffic. The project covers a broad range of dist

YDB is a distributed SQL database and analytical engine designed for horizontal scalability and strong consistency. It functions as a multi-model system that supports transactional and analytical workloads through a distributed architecture providing serializable ACID transactions. The system is distinguished by its broad protocol compatibility, implementing the PostgreSQL wire protocol for standard SQL drivers and the Kafka protocol for messaging and streaming. It further serves as a vector database, supporting vector indexes and approximate nearest neighbor searches for semantic search and

TiKV is a cloud-native distributed transactional key-value store and storage engine. It provides a distributed database designed for horizontal scalability and strong consistency across a cluster of physical nodes. The system uses a Raft-based consensus mechanism to maintain data availability and state synchronization. It ensures ACID compliance for distributed transactions through a two-phase commit workflow and manages data distribution via multi-Raft sharding. The engine handles massive datasets using automated range splitting and cluster load balancing to distribute data across different

This project is a high-performance MQTT broker and IoT data platform designed to manage millions of concurrent device connections. It provides a scalable infrastructure for ingesting, processing, and routing telemetry data across distributed systems, utilizing an actor-based concurrency model to maintain high availability and state synchronization across cluster nodes. The platform distinguishes itself through integrated stream processing and edge computing capabilities. It allows users to execute declarative SQL-based rules directly against incoming message streams for real-time filtering, t

phpredis is a C-based native extension that bridges PHP applications with Redis servers for high-performance data storage and retrieval. It serves as an interface for manipulating strings, hashes, lists, sets, and sorted sets while providing a direct path for executing Redis commands and server-side scripts. The extension provides comprehensive support for distributed environments and high availability. It interfaces with Redis Cluster to distribute data across multiple nodes using hash slots and manages Redis Sentinel for service discovery and automatic failover. It also enables shared state

uWebSockets is a high-performance networking engine providing an HTTP web server and a WebSocket server framework. It implements a multi-threaded event loop architecture to deploy isolated application instances across multiple CPU cores and includes an SSL/TLS network layer for secure, encrypted communication. The project features a dedicated WebSocket pub/sub engine for distributing messages to specific groups of connected clients. It optimizes network throughput through syscall corking to reduce kernel overhead and employs payload compression to minimize data transfer sizes. The system cov

pgdog is a PostgreSQL sharding proxy, distributed SQL router, and connection pooler. It is designed to enable horizontal data distribution by splitting tables and indices across multiple independent servers to scale storage and processing capacity. The project distinguishes itself through online resharding capabilities, using logical replication to move data between shards without application downtime. It supports multiple routing strategies, including hash, list, and range-based query routing, and manages distributed atomic transactions using a two-phase commit process to ensure consistency

Iggy is a distributed message streaming platform and multi-protocol message broker that functions as a persistent distributed log store. It provides infrastructure for publishing and consuming binary messages using an append-only log, ensuring high availability and data consistency across nodes through Viewstamped Replication. The platform is distinguished by its specialized LLM streaming infrastructure, which uses a server protocol to connect large language models to streaming data and system controls. This includes standardized protocols for context management and data bridging via HTTP or