Redis: an open source in-memory data structure store
Redis is an open source, in-memory data structure store, used as a database, cache and message broker. It supports data structures such as strings, hashes, lists, sets, sorted sets with range queries, bitmaps, hyperloglogs and geospatial indexes with radius queries.
Redis has built-in replication, Lua scripting, LRU eviction, transactions and different levels of on-disk persistence, and provides high availability via Redis Sentinel and automatic partitioning with Redis Cluster.
Many popular languages use Redis bindings, including: ActionScript, C, C++, C#,Java, JavaScript (Node.js), Perl, PHP, Pure Data, Python and Ruby.