There are a number of sets of rules that I have written, or am in the process of writing in some cases. Mostly these are wargame rules, often for low level infantry combat. There are also other systems for different sorts of games.
"Wargames are played, for the most part, without the supervision of an umpire. The game relies on the integrity of the individual players to show consideration for other players and to abide by the rules. All players should conduct themselves in a disciplined manner, demonstrating courtesy and sportsmanship at all times, irrespective of how competitive they may be. This is the spirit of the wargame."
Bob Cordery, Wargames Development.