The personal Ancestry File (or PAF) is a geneology program (i.e. Family Tree Maker). It's pretty much considered a staple of any die-hard ancestor-hunter because, although it may be clunky, it's the best there is -- it was origionally written for/by the the LDS Church (the Mormons) who have a god-charged quest to research their family history, and the PAF is one of the tools they've come up with in their 150 years of geneologic research.
The last version I saw in person was the (version 2?) MS-DOS based version, distributed until 1995 (IIRC) that would run on anything that could vaguely be considered MS-DOS compatible. The new versions, I'm told, are finally aquiring a mystical property call 'user friendly-ness'.