If you're interested in programming, you may want to take a look at Core War. In this game, you write a program which then duels against programs written by other people. There seem to be several different versions of this program for different operating systems. It's sort of like programming a robot which then battles with other robots to see which one is best. The programming language is based on assembly, which is definitely not easy to learn! Overall, it's not for novices!
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