ComputerCraft

ComputerCraft is a Tekkit mod that adds computers, modems and Turtles to the game. The computer can be progrogrammed in the programming language LUA. There are severall LUA Api's in this mod, that can let you do things, like manupulating redstone using a computer.

Computers
Computers are blocks, that, when just placed, does abselutely nothing. But when you right-click a computer, a black screen pops up, and you can use it! Computers are fully programmable, in the programming language LUA.