Lua is a very interesting, tiny programming language which has come to be quite popular for game development and other fields where customization is desired. The entire language can be learned in a few days, yet the language has been thoughtfully designed to allow very abstract meta programming.
On this page you can interact with a Lua Shell aka REPL, helpful if you're just learning or want to run some quick experiments.
Note: This tool uses open source code from Lua. The original code is available on their website under the MIT license. github here.