Redis is an open source, in-memory data structure store.
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 different levels of on-disk persistence and a Pub/Sub messaging system.
In computing, a cache is a component that stores data so future requests for that data can be served faster
Message broker is an intermediary program module which translates a message from the formal messaging protocol of the sender to the formal messaging protocol of the receiver.