Custom ASP.NET providers which use db4o as back-end. Beginning with Membership Provider, Role Provider, and Profile Provider. Code is based on MSDN sample code and is unit-tested. Version 2.0 uses db4o 8.0 and C# 4.0.
IMPORTANT: If you plan to use db4o in an ASP.NET web application, understand that db4o requires FullTrust .NET security permissions (because it depends on reflection and unmanaged code), which many shared hosting providers do not provide to your web application.
However, there are some shared hosting providers that will run your web app with FullTrust; I am told that http://www.ihostasp.net does so, but I have not tried it myself. It is simply the first one I found when googling.
Also, it has been reported that this does not work on Mono, though I have not looked into it myself.