Are there any small scale, durable document/object databases?

I have a few .Net projects that would benefit from using a document/object database opposed to a relational one. I think that db4o would be a good choice, but we're not sure how much the cost is. I'd love to use MongoDB but it's design isn't for small scale, single server applications.

Are there other options out there that I just haven't run across for small scale applications?

EDIT: So is this a space that doesn't have a good solution, yet? Are there no smal开发者_如何学编程l scale & durable document databases? Would my best choice be to use MongoDB and set the --syncdelay option set to 1?

BerkeleyDB is pretty good.

if, it's really very small scale, just serialize/deserialize it yourself :) or create a document based structure in an embedded relational database like SqLite...

So RavenDB looks to fit what I'm looking for. I played around with the source and gave it a spin. It's a mix of CouchDB and MongoDB. The main difference is that it uses the ESE engine built into Windows which provides crash recovery, which is mainly what I'm looking for. According to Ayende's Blog there's still much more to be done before it's released, but it's fun to follow along from GutHub.