I’ve been developing a highly modified version of Lua (including a rewrite of the sources to keep a better maintainability). Right now i’m at a point where I would consider forking Lua, and possibly re-release it under a different name (so people don’t mistake it as the original Lua interpreter).
Of course the resulting Interpreter and compiler will be Opensource (MIT License, just as Lua5.0). but I wonder if that would be just fine with the Lua license? Can I use the Lua sources to continue my own work? do I have to keep the copyright notes?
My first suggestion would be to send an email to the Lua folks. I’m 99,9% sure you won’t have any problem.
Now that I think about it, another guy create a language called “Idle” which, if I remember well, is heavily based on Lua.
As long as you properly show the due credits and fairly represent the differences with Lua, I’m sure you’ll be fine.