KBioritmi is a biorhythm generator for KDE. It includes a Kicker applet that shows biorhythm graphs for seven days before and after the current date, a standalone application that can show the biorhythm of a selected date and export it in CSV format, and a Coupler, which can be used to couple your biorhythms with those of another person such as your partner.
Tux Paint is a simple and entertaining drawing program geared towards young children. It has a simple interface, sound effects, and a cartoon character (Tux, the Linux penguin). Along with drawing brush strokes, lines and shapes, you can also enter text and place "rubber stamp" (or "sticker") images on the picture. Tux Paint is extensible, and could be useful in an educational environment (such as a grammar, elementary, or grade school). It's portable across numerous platforms, and runs well even on slower systems like the Pentium 133MHz.