OpenGrade is open-source software for teachers to keep track of grades. It runs on Linux, as well as some other operating systems.
An applet that shows the locations of the planets, stars, moon, and sun in the sky from any location and for any date and time.
Spotter is a program that lets students check their answers to math and science questions. It handles symbolic as well as numerical answers. The software is free and open source.
When is an extremely simple personal calendar program, aimed at the Unix geek who wants something minimalistic. It can keep track of things you need to do on particular dates.