redis

A persistent key-value database with built-in net interface written in ANSI-C for Posix systems

Redis is an advanced key-value store. It is similar to memcached but the dataset is not volatile, and values can be strings, exactly like in memcached, but also lists, sets, and ordered sets. All this data types can be manipulated with atomic operations to push/pop elements, add/remove elements, perform server side union, intersection, difference between sets, and so forth. Redis supports different kind of sorting abilities. 

Basho Riak: An Open Source Scalable Data Store

Why use Basho Riak when established approaches like RDBMS have been good enough, mostly? We can think of only one reason: because building scalable, fault-tolerant, and highly-available applications should be simple and inexpensive.
With Basho Riak, we built an alternative to the RDBMS in the typical application stack. When you choose Riak to store your data you will discover:

• Applications scale predictably when running Riak.
• Riak makes applications fault-tolerant .
• The meaning of complete availability.
• Riak reduces expenses. We guarantee it. Contact us to learn how Riak can significantly lower your database and operations expenses.

Achieve complete availability for your applications at a fraction of the cost with Basho Riak.

Membase

Membase is a distributed key-value database management system, optimized for storing data behind interactive web applications. Membase automatically spreads data and I/O across servers. This "scale out" approach at the data layer permits virtually unlimited growth of transaction capacity, with linear increases in cost and constant per-operation performance