Redis

Redis is an in-memory data structure server that holds values in strings, hashes, lists, sets, sorted sets, and streams, and serves them over the widely supported RESP protocol. It covers caching, session storage, counters and rate limiters, job queues, and pub/sub, with optional persistence through snapshots or an append-only log and replication for availability.

Applications reach for it whenever a round trip to disk-backed storage is the bottleneck, especially in request paths, real-time features, and lightweight queuing.

Running it on your own hardware keeps session data and cached responses inside your infrastructure, with no metered command pricing and simple snapshot options.