LuaCLR is a compiler for the Lua 5.1 language (http://www.lua.org) that targets Microsoft's Common Language Runtime (and should also work under Mono). It's implemented mostly in Lua and is using the Lua 5.1 interpreter to bootstrap, with part of the runtime system in C#.

The goals of the implementation are completeness (being as faithful to the semantics of the Lua interpreter as possible) and speed.