This is the Gtk interactive geometry software. It allows one to create geometric figure plus the interactive manipulation of such figure in respect with their geometric constraints. It is usable in teaching situation with students from primary or secondary level.

mtr combines the functionality of the 'traceroute' and 'ping' programs in a single network diagnostic tool.

ed is a line-oriented text editor. It is used to create, display, modify and otherwise manipulate text files.

Crafty is the strong chess program played on ICC. It uses all of the search algorithms you have probably read about and performs better than gnu-chess in most positions. It has a reasonable set of features to use, and offers a great starting point to try your own new search extensions.