What is Redis?
Redis™ (REmote DIctionary Server) is an open-source, networked, in-memory, key-value data store with optional durability. It is often referred to as a data structure server since keys can contain strings, hashes, lists, sets and sorted sets.
Comments and Reviews
Said about Redis as an alternative
Redis can run on Windows(https://github.com/MicrosoftArchive/redis/releases) & Linux based systems. NCache is only for Windows .NET. And we have a combination of Linux/Ubuntu systems.