Take a look at RavenDB. It looks as though it can be embedded and is schemaless and works with .NET
From the website:
- Scalable infrastructure: Raven builds on top of existing, proven and scalable infrastructure
- Simple Windows configuration: Raven is simple to setup and run on windows as either a service or IIS7 website
- Transactional: Raven support System.Transaction with ACID transactions. If you put data in it, that data is going to stay there
- Map/Reduce: Easily define map/reduce indexes with Linq queries
- .NET Client API: Raven comes with a fully functional .NET client API which implements Unit of Work and much more
- RESTful: Raven is built around a RESTful API
