This is content taken from the 2009 StackOverflow DevDays conference in Austin, Tx.
CouchDB is a robust document-oriented and schema-free database server. CouchDB was written in Erlang which was designed for the Telecom industry. This means that CouchDB has excellent concurrency, message handling, and reliability.
The most exciting thing about CouchDB actually stems from their motto, "Relax". As a programmer, you can relax knowing that in the event of a database server crash, not only is your data preserved - because data is never overwitten in CouchDB, new files are created - but the CouchDB server (being a product of Erlang) will simply start itself back up and continue with business as usual. In fact, the shutdown command of some versions of CouchDB is a simple kill -9.
CouchDB is especially unique because it doesn't just scale-up for larger applications, but it also scales down extremely well to create a very lightweight implementation that can be used on mobile devices and netbooks.
Sound interesting? Give Damien's talk a listen and see if CouchDB is the right choice for your next project.