Hi!

We use EntitySpaces www.entityspaces.net

It is really light and super fast. It has the best Persistence Layer and Business Objects model for Microsoft .NET that I have come across.

A snippet from their webiste:
"From mobile devices to large scale enterprise solutions in need of serious transaction support, EntitySpaces is the development tool that can meet your needs. Whether you’re writing an ASP.NET application with medium trust requirements, or a Windows.Forms application, the EntitySpaces architecture is there for you. EntitySpaces is provider independent, which means that you can run the same binary code against any of the supported databases. EntitySpaces is available in both C# and VB.NET. EntitySpaces uses no reflection, no xml files, and sports a tiny foot print of less than 200k. Pound for pound, EntitySpaces is one tough .NET architecture."

If you need more information let me know.

Sarosh