[icey]

"Raven is an Open Source (with a commercial option) document database for the .NET/Windows platform."

I'm not sure it's a competitor at all. RavenDB is a CouchDB clone for .Net that requires a commercial license for proprietary software.

[latch]

Which has a ton of magic baked into the driver making it unlikely you'll get your data back out via anything but .NET.

[rkalla]

Well put.