Included in most of the tech mod packs but deserving of a special mention is ComputerCraft, which allows you to program computers and robots in Lua that can interact with the Minecraft world!
CC is the reason I can write some Lua, at least after the initial intro when I was fumbling around in the TES 3 editor. I went down that rabbit hole and build some far too complex one-off things. One of them even called out to a PHP backend for a shared database. I think I started hacking on a system that could propagate updates between CC nodes in a sort of mesh network (wireless CC networks) before just using the database backend. Luckily I lost interest before writing a whole network layer.
