Vignette is a simple and flexible RPG from Nathan Russell. He uses it for a wide variety of genres and settings. There are some concepts here to steal for the more RPG based miniatures games.
Warstuff is a set of one page rules for playing games with whatever you have in your box. The author writes:
WarStuff is a single-paged ruleset designed to be played with any miniatures or toys you have at hand. The rules are perfect as an introduction to wargaming for kids, and for conventions and pick-up games where players might have models from different lines.
Shawn Garbett has written GEM — the Generic Easy Miniatures Rules — which seem to be aimed at larget miniatures in a skirmish scenario. Garbett writes:
GEM is specifically for those who are sick of having new revisions of their favorite rule system leave out those great new miniatures they just finished painting. If all the commercial miniature systems have flaws which you really don’t like, then GEM may be just what you’ve been looking for. If you’ve ever been bogged down in rolling and rolling with no resolution in sight, GEM is probably for you. Several other play options exist, for customization to a gaming groups own tastes.
Imaginality is a universal RPG where the action is resolved by playing a card from a hand of seven. This adds an additinal element of strategy, because payers get to decide when they REALLY need to succeed, and when they can afford to take a risk, or live with a lesser success.
Fight Dice is a set of free wargames rules that uses a neat dice pool system, where the players allocate handsfull of six sided dice to their actions.