SmallBASIC is a free, cross platform BASIC on SourceForge. SmallBASIC runs on Windows, Linux, DOS, PalmOS and Nokia 7790. It is a great tool to teach programming or just for tinkering.
I have it on my home computer and on my Palm Pilot. I originally downloaded it to teach programming to my kids. Instead, I have been playing with it. Once I start working on a program, I don’t like to stop. I keep thinking of new features to add or ways to make it work better.
That’s OK, the kids have been more interested in finding guitar tabs on the internet and playing the flight simulator than programming.
If you enjoy programming, SmallBASIC is almost too much fun.