The predicted consolidation of the NoSQL database landscape has begun. Membase and CouchOne have announced that they are merging to form Couchbase.

And in more interesting NoSQL news, Danish IT company Trifork has announced that it has acquired an 8% stake in Basho as part of the NoSQL vendor’s $7.4m series D round, and has become the European distributor for Riak.

The formation of Couchbase brings together to of the leading companies in the NoSQL space, and the complementary nature of the their technology and business plans highlights that the term NoSQL has been applied to many different database technologies which are being adopted for different reasons.

While Membase had focused on improving the performance of distributed applications through its Membase Server distributed database, CouchOne focused on developer interest in flexible document data stores and mobile applications, rather than performance at scale.

Additionally while Membase was focused on operational adoption with a small (albeit significant) developer community, the priority with CouchOne has been on growing adoption of Apache CouchDB, with commercial efforts only recently becoming the focus of attention.

The technology is also complementary. Couchbase will combine the Membase and CouchDB projects to form a new distributed document store project of the same name that combines the caching and clustering technology of Membase with the CouchDB document data store.

The result will be a new distributed document database covering a variety of use cases from mobile applications (Mobile Couchbase) to scalable clusters (Elastic Couchbase), with synchronization of data between the various Couchbase implementations enabled by CouchSync.

The merged company will be led by Bob Weiderhold, formerly CEO of Membase, while Damien Katz, formerly CEO of CouchOne and creator of the CouchDB database, becomes CTO.

Couchbase is claiming more than 200 customers, which would indicate phenomenal growth for both companies since the launch of their CouchOne Mobile and Membase Server products in September and October 2010 respectively.

Prior to the launch of those products they previously claimed just a handful of customers each, although CouchOne had signed up thousands of users to its free hosted services, so it had a large and willing audience ready for conversion.

Additionally the company claims millions of combined users since CouchDB has been included in every installation of the Ubuntu Linux distribution since late 2009 and Heroku (now part of Salesforce.com) offers a Membase-driven service to thousands of its hosting customers.

We previously predicted that we would see the NoSQL market both consolidate and proliferate this year, and it is worth noting that the merger of CouchOne and Membase will not result in a similar consolidation of open source projects.

While Couchbase.org can be expected to replace membase.org over time, the Couchbase project will be independent of the Apache CouchDB, which will not be impacted by the merger. Couchbase will continue to contribute to both CouchDB and also the memcached project.

While we’re on the subject of NoSQL, it is also interesting to see that Danish IT vendor Trifork has not only signed up to be European distributor of the Riak database, but has also taken a stake in Basho Technologies.

Trifork has acquired newly issued shares in Basho representing 8.35% of the company as part of its series D round, with an option to acquire an additional 3.96% at the end of Q1 2011.