Mono.Cecil is a library to generate and inspect programs and libraries in the ECMA CIL form.
To put it simply, you can use Cecil to:
Cecil has been around since 2004 and is widely used in the .NET community. If you're using Cecil, or depend on a framework, project, or product using it, please consider sponsoring Cecil.
To discuss Cecil, the best place is the mono-cecil Google Group.
Cecil is a project under the benevolent umbrella of the .NET Foundation.