Lua
From Mario Fan Games Galaxy Wiki
Lua is a kind of scripting language known as an extension language. Though standalone programs can be coded entirely in Lua, it is intended to be used as a way for users of a program to easily add functionality through scripts. Lua extensions exist for MMF2, and a few users of said program use it as a way of working around MMF's lack of a scripting language. A Lua script can also run faster than an equivalent script made through MMF's event editor. Retriever II is one MFGGer who has used the language extensively, even submitting howtos and creating an NCFC booth about Lua.
It is possible that many fangames will implement Lua in the future, some proposed games include: