Redis
An in-memory data structure server used as a cache, message broker, and document and vector query engine for real-time applications.
Redis is an in-memory database that stores data as strings, lists, sets, hashes, sorted sets, streams, and JSON documents, exposed with high-level semantics such as counters, queues, leaderboards, and rate limiters, plus transactions and scripting.
It is used as a distributed cache with eviction policies and expiration, a session store, a NoSQL key-value and document store, a search and query engine over hash and JSON documents with vector search, full-text search, and geospatial queries, and an event store and message broker built on lists, sorted sets, sets, and streams with publish and subscribe.
It also supports retrieval-augmented generation and semantic caching workloads for AI applications. Redis is written in C.