It is a Lua engine for TC. It gives you ability to make scripts with Lua language which will make the development process more faster and flexible. I am not a fan of lua but, the true is very that ELUNA can be useful for small scripts like quests, events, npcs and such. Ofc it can be used for very difficult scripts also. I think you can reload the engine in-game which is very useful for testing purposes during the development process.