Lou Coatney offers Stalingrad Attacked, a free, complete board wargame. Coatney is a veteran game designer with a number of published designs, including Dark Crusade.
Majestic 12 games has these demo rules for their Grand Fleets miniature wargame. My group has played these and really enjoys them. Majestic 12 explains:
Grand Fleets is a comprehensive miniatures game of dreadnought-era naval warfare. In addition to rules for everything from ships to aeroplanes, Zeppelins to submarines, the rulebook includes:
Data cards for over 120 ships, plus guidelines for converting any ship of the period to game values; Eight scenarios encompassing conflicts from the Sino-Japanese War of 1894 through the opening salvoes of World War Two, including several variants; Fifteen pages of weapon data, covering all major gun and torpedo models in use through 1939, over 200 aeroplanes, and more than 20 airships; and Optional rules for flotillas, night-fighting, smokescreens, and more!
Hurrah Stalino! is a set of corps to army level rules for the Eastern Front in World War II.
Lion’s Lair is a free print-and-play board game from Lou Coatney. He describes it as:
A fast-playing, point-to-point game of the British trying to battle their way through U-boats, Italian subs, Italian aircraft, German StuKas, Italian MAS motor torpedo boats, and the Italian fleet.
Schnell Rules is a set of fast play rules for WW2 coastal forces.