Why Redis? When Memcached?

What is Redis and what is Memcached? Why use Redis and when Memcached? Way we can call Redis a NoSQL database? Today I want to present my conclusions about which cache engine to use? Redis versus Memcached.
What is Redis and what is Memcached? Why use Redis and when Memcached? Way we can call Redis a NoSQL database? Today I want to present my conclusions about which cache engine to use? Redis versus Memcached.