Is it possible to use MongoDB as an embedded database?
There is no way to embed MongoDB right now - but on the wishlist of many people.
You should consider EJDB.
EJDB is the C library based on modified version of Tokyo Cabinet. JSON representation of queries and data implemented with API based on C BSON, MongoDB-like queries and overall philosophy.
I like tokyo cabinet. It is flexible document storage like mongodb. It also comes with some nifty full text searching abilities and a small memory footprint.
Tokyo Cabinet:http://fallabs.com/tokyocabinet/
I've also created an objective-c wrapper (in case you wanted to embed it in an osx/ios app).https://github.com/isaact/TSDocDB