Over a year ago I ran across CouchDB - a NOSQL database that runs over HTTP and programmable via REST.  I was intrigued by its power and flexibility at the time, but here are a few things I didn’t realize:

• CouchDB can support queries across millions of rows in less than a second.
  • In fact, I have queried 16 million rows faster than I could time it by hand
• CouchDB can both store your data *and* your application
  • Check out CouchApp to learn lots more
• CouchDB can support data validation and user authentication.
• You talk to CouchDB using C#, Java, Ruby, Python, JavaScript, PHP, etc
• CouchDB supports etags for data caching

Check out the definitive book here: CouchDB: The Definitive Guide