RethinkDB vs. Riak vs. ClustrixDB

RethinkDB is built to store JSON documents, and scale to multiple machines with very little effort. It has a pleasant query language that supports really useful queries like table joins and group by, and is easy to setup and learn.

Riak is a distributed database designed to deliver maximum data availability by distributing data across multiple servers. As long as your client can reach one Riak server, it should be able to write data. In most failure scenarios, the data you want to read should be available, although it may not be the most up-to-date version of that data.

ClustrixDB is a scale-out SQL database built from the ground up with a distributed shared nothing architecture, automatic data redistribution (so you never need to shard), with built in fault tolerance, all accessible by a simple SQL interface and support for business critical MySQL features – replication, triggers, stored routines, etc.