This is a Free-as-in-Rootbeer desktop database for keeping track of one family's genealogy. Earlier versions (not listed here) were sold commercially for 16-bit DOS, Macintosh and Apple II, but the church bought the publisher out and made later versions available at a token charge or for download. PAF 3 was a 32-bit DOS (DPMI) program that works well under Dosemu. Even though it's free, PAF is well-designed and useful. Many features facilitate fast data-entry and support careful research practices.
New major versions have generally been able to read the data files from one version back, but all versions have supported import from and export to the publically-documented GEDCOM format.
Most other genealogy programs, including the Linux native ones, support import and export of GEDCOM data.
Currently, not everything works under wine (check the bug database and per-version comments for details).
There are a couple of Linux alternatives:
Gramps (Debian package) - XML-based, written in Python. Good data-model (reads all of GEDCOM 5.5), handles large family trees well
GeneWeb (Debian package) - Written in OCaml, with CGI interface. Simpler data-mode, but handles 400k-name families without trouble.