From Mac Guides
GarageBand is Apple's consumer-grade music editing/creation software. It is part of the iLife suite.
First released as part of iLife '04 in January 2004, GarageBand aimed to be a cheap and easy way for Mac users to create and record their own music. It removed all the hassles of previous music-making software and allowed anyone to produce a tune, while still allowing seasoned musicians to create stunning works without limit. A full range of software instruments are provided with the software, along with many realtime effects for live guitar recording and more. Several add-on "Jam packs" have been released to increase the number of loops, effects and software instruments available. Saved songs can then be exported to iTunes and transferred to an iPod or burnt to a CD. The software is hardware-intensive and requires a reasonably fast G4 or better to run adequately.
There are currently a number of Jam Pack add ons for GarageBand. These add additional software instruments, presets and loops.
Version 5.0, released January 6, 2009 as part of iLife '09.