RLua

It contains almost the full coverage of the Lua C API, seamless translation of Lua and Ruby objects into each other and calling functions of each language from other one.

Hashes and Arrays are translated recursively: all keys and values are translated too.

Getting any Lua function to Ruby code (even the Ruby proc that was translated
before) results in Lua::Function created, and tables behave the same creating
Lua::Table object.

Proc objects are duck-typed: anything that responds to +call+ method is considered Proc.

Translation of any object not in the list is impossible and will generate an TypeError exception.