Redis is an advanced key-value store. It is often referred to as a data
structure server since keys can contain strings, hashes, lists, sets and
sorted sets.

You can run atomic operations on these types, like appending to a string;
incrementing the value in a hash; pushing to a list; computing set
intersection, union and difference; or getting the member with highest
ranking in a sorted set.

In order to achieve its outstanding performance, Redis works with an
in-memory dataset. Depending on your use case, you can persist it either
by dumping the dataset to disk every once in a while, or by appending
each command to a log.

Redis also supports trivial-to-setup master-slave replication, with very
fast non-blocking first synchronization, auto-reconnection on net split
and so forth.

Other features include Transactions, Pub/Sub, Lua scripting, Keys with a
limited time-to-live, and configuration settings to make Redis behave like
a cache.

You can use Redis from most programming languages also.