TripleA is a free turn based strategy game and board game engine. Has single player vs ai/hot-seat, multiplayer through Play By Email, network play, and a hosted online lobby. Comes with 4 games, and over 100 more games and maps that can be downloaded from the user community. It is open source, needing only Java 5 to run (can run on Windows, Mac, Linux, etc). Supports features such as savegames, encrypted dice gen, low luck, and many other options.
One of the most complex maps and games created yet for TripleA. Has politics, special units like airfields, harbors, different sized factories, a custom technology tree, and special rules for situations like lend-lease, russian winter, etc.