Reflexil is an assembly editor and runs as a plug-in for Red Gate's Reflector, a great tool for .NET developers. Reflexil is using Mono.Cecil, written by Jb Evain, which is a strategic library for the Mono project.
Reflexil is able to manipulate IL code and save the modified assemblies to disk.
... [More] Reflexil also supports 'on the fly' c# code injection. [Less]
dylan.NET is a programming language still in its infancy, trying to make .NET programming more available to linux and windows (even Mac OS/X) based systems. The goal is to have a command line compiler that does NOT need fancy IDEs in order to provide great functionality.