Software that will entertain a 10 year old boy for hours...

[MidwestStuck]

No matter what, don't start teaching html to him like my fourth grade teacher tried to do with our class over ten years ago. I can't think of any specific programs, but definitely do something simple, visual, and interactive.

 

[jayeskreezy]

PhotoBooth and iConquer. I got it in the macheist giving tree and all of my friends love it.

looks like Risk. At first I was going to suggest reading a book, but making a movie or photo creation can be both productive and educational. I'd turn off the internet though.