(This is an expansion of an idea Jota came up with and a few other people made suggestions on)
In I Am Legion the players each make up part of a mighty, multi-talented hero — someone of the scale of Conan, Zorro, or Superman. The game works as follows:
The players and GM agree on a one-sentence premise for the character and setting ("The character is a superhero crime-fighter on the streets of Gotham") and then, in turn, each player gives a boast or two for the character ("I strike fear into the hearts of criminals everywhere!" "Whenever my sign appears in the sky, I am there!" "No man catches me unawares or unprepared!"). After this roughly establishes the character, the group should agree on some more details: name, gender, a little more backstory, and so on.
Next the players choose which aspect of the character they'll take on — this can something be hinted at in a boast, or something new ("I am his Intimidating Personality" "I am the Equipment he is never without" "I am the symbol of the Bat"). When they choose an aspect, they also choose a persona to represent it — someone's Aggression might go with a persona of Frank, their old boxing mentor, or it might be the character themself, eight years old, scared and lashing out.
With this all set, numbers can be assigned. The character has four stats: Toughness, Intelligence, Agility, and Charm*. The players can divvy up 12 points between them, figuring a score of 2 is pretty good but not exceptional for the setting, and 5 is truly amazing.
*Note that these shouldn't overlap too much with players' aspects — if they do, swap out a stat for something else. For that matter, feel free to swap out stats to match the setting anyway; the point is for the stats used to 1) relate to things the character will be doing 2) be useful with most of the aspects players have chosen 3) be "passive" in themselves.
The players then fill out their individual personas. They each have eight skills and 20 points to distribute across them (the average person who does a thing for a living has a 2 in the skill, unless it's a really hard thing). Note that multiple players can take the same skill; this is useful later. Skills here are essentially ways of using the aspect — Intimidating Personality might go with skills of Interrogation, Deflecting Blows ("His eyes! They turn my bones to water!"), Concentration, and so on.
That's probably it! Maybe the players should also pick signature moves or stunts or something, but not right now.
Play works like you'd expect, although note that in this system you explicitly don't do any action until everyone agrees to go ahead — typical play should be like "Ok, we leap across the room and kick the first thug in the face" "While we do that, we grab a tear-gas container from my belt and toss it behind us" "Before any of that happens we shoot out the light" "Uhh..." "Ok, fine, we don't do that until we've finished leaping" "Great, let's do it."
In normal skill resolution, you add your skill to the GM-decided-on corresponding stat, and roll that many d6s, counting 5s and 6s as successes, and try to get however many successes the GM's specified. Usually 1 for a basic success, and more or better or faster effects for every success beyond that (eg, 1 success to punch out one thug and 2 to punch out two; 1 success to pick a lock, 2 to pick it quickly).
Players can work together on actions in three ways:
That's basically it! The character probably has a health track equal to their Toughness, and when it's gone they're knocked out. Fighting is probably an attack roll against an attack roll and taking the difference in successes in health track damage (if the players' roll is lower; if it's higher, obviously the opponent takes damage, or mooks are eliminated).