Nice, but no continuing development
There seem to be a scarce few contact managers on Linux for personal use (at least as a contact manger on it's own, and not in part of a huge PIM package).
yqpim is a small, simple program that allows you to track contact information and keep notes - it's simple and seems to work well.
However, this beta hasn't had any work done on it since January of 2002.
An open, cross-platform journaling program.
A scientific plotting package.