About “Not Only SQL”…
We could say that it’s the next Generation Databases mostly addressing some of the points: being non-relational, distributed, open-source and horizontally scalable.
We can find a lot of new databases of this type like:
API: Memcached API+protocol (binary and ASCII) , most languages, Protocol:Memcached REST interface for cluster conf + management, Written in: C/C++ + Erlang (clustering), Replication: Peer to Peer, fully consistent, Misc: Transparent topology changes during operation, provides memcached-compatible caching buckets, commercially supported version available.
JSON based, Document store database with compiled .net map functions and automatic hybrid bitmap indexing and LINQ query filters
Embedded JSON database engine based on tokyocabinet. API: C/C++, C# (.Net, Mono), Lua, Ruby, Python, Node.js binding, Protocol: Native, Written in: C, Query language: mongodb-like dynamic queries, Concurrency: RW locking, transactional , Misc: Indexing, collection level rw locking, collection level transactions, collection joins., License: LGPL