A free Mastermind clone written in C. The source code is smaller in size than the copy of the GNU GPL included in the distribution.
Download version 1.1 here. To compile Dedux you'll need a working version of an ANSI C compiler. Not a big deal.
Q: What is Dedux? A: Dedux is a nifty little C program that plays a Mastermind-like game with numbers. It is something I did just for the hell of it, and I have made the code available free-of-charge under the terms of the GNU GPL. Q: If Dedux is like Mastermind, then what is Mastermind? A: Mastermind was originally a board game for two, played with colored pegs. One player randomly chooses four pegs and places them in a special pegboard, which keeps the four-peg "code" secret from the other player. That player has ten tries to match the code, by presenting four-peg sequences to the first player; the codekeeper gives clues as to which colors appear in the secret code and whether or not they are in the correct place in the code. It's easy enough for children to play, but can be extremely challenging. Q: What's up with the name? A: I called it Dedux because I figured either the Mastermind name was copyrighted, or any clever variation on that name that I could come up with would already be taken. The program is so named because you must use your skills of "dedux-ion" in order to win.