Actually I think Lua is a great candidate because of its openness and its similarity to C (predominant systems OS programming language).

Lua is open, as their about page (http://www.lua.org/about.html) states:

Lua is free

Lua is free open-source software, distributed under a very liberal license (the well-known MIT license). It may be used for any purpose, including commercial purposes, at absolutely no cost. Just download it and use it.