Redis
In-memory key-value storeOpen source· verified Sep 2026
An in-memory data structure store used as a cache, session store, rate limiter, queue, and pub/sub broker. Responses are typically sub-millisecond because data lives in RAM.
Official site
Reach for it when
- Caching and sessions
- Rate limiting
- Pub/sub and lightweight queues
Worth knowing
Licensing changed in 2024 and AGPLv3 was added in 2025; Valkey is the BSD-licensed community fork.