Redis

Redis is an open-source in-memory data structure that is used as a database, cache, and message broker. It caters to developers who require high performance and flexibility. The main features of Redis include the ability to store and retrieve different data types such as strings, hashes, lists, sets, and sorted sets. It also provides features such as replication, LUA scripting, LRU eviction, transactions, and various levels of on-disk persistence. The pricing model of Redis is open source and free of charge. However, there are also paid versions with additional features and support.