Table of contents
ObjC# is a transparent two way bridge that allows the CLR to access the rich underlying ObjectiveC frameworks as well as providing direct access to the CLR frameworks from the ObjectiveC language.
IKVM is a framework required to host and interface with Java byte code on top of the MS .NET and Mono runtimes.
GAPI is a xml based code generator included in GTK#, to build bindings (ussally) completely 100% cli based bridges to many different GObject and GLib classes.
Simplified Wrapper and Interface Generator (SWIG) is a code generator that builds bindings for many languages including C# to communicate with C and C++. (It should be noted that most nearly all C interfaces can be handled by the built-in p/invoke interfaces without the need to use SWIG to do this)