Redis is an open source in-memory data structure. Redis fits well for a database cache and is not common, but it can be used as a message broker using the publish-subscribe feature, it can be useful to decouple applications.
There are some interesting features supported by Redis such as transactions, atomic operations, and support for time-to-live keys. Time-to-live is useful for giving a time for the key, the eviction strategy is always hard to implement, and Redis has a built-in solution for us.
