Ahnenblatt (german, "ancestral sheet") is a software for genealogical research. You can enter lots of data about single persons and then create family trees and tables.
There are a couple of Linux alternatives:
Gramps (Debian package)
- XML-based, written in Python. Good data-model (reads all of GEDCOM
5.5).
GeneWeb (Debian package) - Written in OCaml, with CGI interface. Simpler data-mode, but handles 400k-name families without trouble.