ComputerCraft

ComputerCraft is a mod by dan200 that adds computers and assorted peripherals to your minecraft world. All devices are programmable with the easy to learn Lua scripting language. You can use Redstone and even RedPower 2 alongside your computers, specifically the Red Alloy Wire, and bundled cable allowing for many advanced uses. These computers have Redstone, computation, and even wireless communication support as part of the mod.

Turtles
A Turtle is just like the normal computer,except with its own API. They have the ability to mine out large sections of earth, or simply move items throughout a house. Equipping a turtle with a diamond pickaxe gives it the ability to collect resources.

Turtles use the Turtle API to move and interact with the world.

Programming
Programming in ComputerCraft is accomplished by the use of scripts made on each computer/turtle. each computer follows most of the specifications of lua. the only difference is that computercraft has a API that allows increased interactiveness with a minecraft world. the API allows interfacing with redstone wires and Redpower Cables, and with the turtle, allows it to change the very world through breaking and placement of blocks and redstone interaction. One of the main uses of ComputerCraft is control systems, such as password locks for doors, and even automation of a tnt cannon.

Guides

 * Getting Started with ComputerCraft