db4o is the world's leading open source object database for Java and .NET. Leverage fast native object persistence, ACID transactions, query-by-example, S.O.D.A object query API, automatic class schema evolution, small size (http://developer.db4o.com)
OW.NET -- 1-Wire API port from Java (and J#) to C#. Use the Dallas 1-Wire and iButton chips with standard C# using a serial adapter (also CF.net) or the TMEX drivers on the Windows platform. No J# distribution installation required.
The Official port of the STUNNING! CMS/CMFx "Drupal" to the .NET Framework. Combining The greatest open source CMS with the greatest development platform. It will have the same architecture and will support Drupal modules & themes out of the box.