Weaver.NET is a tool for weaving CLI assemblies in .NET 4.0. The tool is available as a .NET library as well as an MSBuild task & script, which can be easily integrated into any existing project files and the overall build process. Code weavers are .NET libraries (assemblies) that implement a given contract to provide manipulation of CIL code at compile-time.

An adapter for Simon Cropp's Fody tool <http://code.google.com/p/fody/> also exists, which allows you to use arbitrary Fody weavers within the Weaver.NET infrastructure. Support for reverse usage (Weaver.NET weavers under Fody) may also become available in the future.