Multi player rules: I need a help!

[has.been]

As well as those already mentioned I would include the following:-
Pony Wars, which is all players on the same side against the system. The rules may be difficult to obtain as they go back quite a way, but the idea can be (& has been by our group)used for lots of scenarios, not just the original U.S.Cavalry versus Indians, but also such things as a few heroes (players) against lots of poor quality enemy (Magnificent Seven/ Seven Samurai/Jedi knights V Storm troopers/A few British survivors V Zulus etc.
OR
Something like a Viking raid. each player controls a few Vikings and it is a race to see who can get the most plunder (sheep/goats/gold/prisoners etc.)
OR
Using a BIG map & counters/small scale tanks, do something like Operation Barbarossa. Each player is a senior German commander & Adolf (the umpire) expects each to advance as far as possible.