valkey

Valkey is a high-performance in-memory data store — a database that keeps data in RAM rather than on disk so that reads and writes are extremely fast. It was forked (copied and independently continued) from the open-source Redis project just before Redis changed to a more restrictive license, making Valkey the community-maintained, fully open-source successor. It is optimized for caching (temporarily storing the results of expensive computations so they can be reused instantly) and real-time workloads like session management, rate limiting, leaderboards, and message queuing.

Valkey works by storing data as key-value pairs — think of it like a giant dictionary where you look up a value by name. Beyond simple strings, it supports rich data structures such as lists, sets, sorted sets, and hashes. It runs as a standalone server process that your application connects to over a network, and it supports clustering (distributing data across multiple servers) and replication (keeping copies for reliability). A plugin system allows developers to add custom data structures.

You would use Valkey when your application needs sub-millisecond data access — for example, caching database query results, storing user session data, or powering a real-time feature like live notifications. It is written in C and runs on Linux, macOS, and BSD systems.