ComputerCraft is a Minecraft mod (with full survival and creative multiplayer support) which adds in-game computers. Each computers comes with its own operating system featuring a host of builtin programs, and can be programmed to do anything you want with the easy-to-use Lua programming language. Each computer has a screen and keyboard, a comprehensive help system, a fully featured file system, two awesome games (including a text adventure based on Minecraft, and a fast paced arcade action game) and the ability to send and receive redstone signals in all six directions (including RedPower bundled cables, allowing for a full 96 bits of I/O).
New in version 1.2, you can now build Disk Drives for your computers, and carry your files around the world on Floppy Disks (or send them down Buildcraft Pipes or RedPower Tubes for the ultimate in automation). To liven up your home, Disk Drives can also act as programmable record players
Table of contents
Build A Computer
Right click on the screen to interact. You're now in the command prompt. Type "help" to get started, then type "programs" to see the list of programs you can run, and try running some of them. Type "help" followed by the name of a program to find out what it does. When you're ready to start creating your own programs, type "help programming", then use "edit" to create programs or "lua" to just start entering code. All the programs and APIs you can call have their own help pages.
For tutorials and more help on programming in ComputerCraft you should visit the official ComputerCraft forums.
Want more? Build a Disk Drive next to your computer, and craft some Floppy Disks:
Put the disk in the drive, go into your computer again, type "list", and you'll see that each Floppy Disk has its own folder. Now you can use the "copy" or "move" commands and the built in "dj" application.
Interaction with other mods
ComputerCraft includes an API to work with Redpower's bundled cables. Type "help redpower" into your computer to see, which lua commands you can use for that.
Lua is the programming code used by the ComputerCraft mod. It's very easy to learn. Tutorials can be found on the page Lua Tutorials.