Black Holes is a strategy game based on the behaviour of real black holes in Space. It's easy to learn but hard to play well. The idea is to create black holes in Space and to capture the stars that fall inside the event horizon. (See, it's even educational for the kids!)
I originally invented it as a board game, but then decided to program a demo version for the PC. The Demo plays quite well and can usually beat me at my own game! You can read more about it here, or just go for it by downloading the demo plus full instructions.
For anyone interested in such things, I wrote the demo in Quick Basic and compiled it as a DOS executable. Have fun, and let me know how you get on!