Now a days redies database is very famous.
Because it is in memory database. in memory databases are the databases who used main memory to store the data they dont have storage management system/engine like mysql.
Redis is nosql database, you can store your data in hash/key-value pair format.
It is very fasr so many big companies like twitter instagram, github, stackoverflow are using redis.
We have opensource redis and enterprise redis (redis labs).
I will keep posting more information about redis in coming blogs.