I could cite Champions for a lot of innovations: First effect-based system, first appearance of advantages/disadvantages, the concepts of Hunteds and Dependent NPC's, the separation of lethal and non-lethal damage as a core part of the game, and hey, the first point-based character generation system. Sure, those were all pretty important, but the one thing I think is overlooked and underrated is the Presence Attack.
What is a Presence Attack? Why it's simply a mechanical system for frightening, intimidating, charming, commanding, or otherwise imposing your will on an NPC without making an actual, physical* attack on them. Presence is a stat that all characters possess (it defaults to 10 for a normal human) and the mechanic is this: Roll 1d6 per 5 points of Presence, compare your total to the target's Presence, then based on how much your roll has exceeded their score various effects can happen, from losing an action as they hesitate to total surrender or obedience. There are situational modifiers - things like being outnumbered can lessen your chances while doing something impressive like bending a steel bar can improve them.
Yes, that's right - a game system known for number-crunching tactical combat has a system that allows a character to walk in a room and tell everyone "get out" - one that works, is fairly simple to resolve, but has rich options that reward player creativity in play - wow that sounds kind of modern! When was that published? 1981?!
I've seen this used in Champions of course, but I've also seen it work in Fantasy Hero, a sort of Rifts-Hero**, a Traveller Hero campaign, and a Mechwarrior Hero. It seems that if you give players a system for doing this kind of thing, at least some of them will try it out! Nothing makes a player feel like a badass more than having their character walk in to a room full of ninjas, say "Leave" and then watching as they do so, clearing the area for the big confrontation with the Overninja. No powers needed, no magic items needed, no special intimidate skill or feat needed - just the character's innate badassery.
There are those who claim this should be strictly a role-playing thing. I disagree. A mechanical framework for interpersonal interaction is not a straitjacket. Sometimes it's what makes certain things possible. I can tell you that without some kind of mechanical yardstick the scenario above would rarely happen in my games - I tend to play my ninjas as overconfident bad guys. I cannot tell you the lengths a player would have to go to in order to overawe a whole group of them like that. With the Presence Attack though, it's not just an arbitrary call by me - it's something a player can investigate, work towards, and invoke on their own initiative with a pretty good chance to evaluate when it's a good idea and when it is not - and those things are what make this system great.
Now I've tended to focus on the fear aspect of Presence Attacks but that is not the only option. There are other ways to use the system too ...
Yeah - that one doesn't come up as much when it's just the guys playing, but Lady Blacksteel has a tendency towards the lesser forms of mind control when it comes to her characters, which adds an interesting angle for the DM. Don't get me wrong, she likes to play badasses too, hers just have more of a curveball to them than most male characters.
Now the thing that is a little disappointing is that more games haven't included a mechanic like this one. D20 games often have some kind of Bluff mechanic, but what if it's not a bluff? What if you are that good? Some of them have an Intimidate skill as well and it can work in a similar way, but few have the non-fear aspect built in as well. Sure, they have Diplomacy or Streetwise, but those have a different flavor to them than having a 30 or 40 Presence would in Hero.
To sum up: More games should have something like this! In level based games it would be really easy to do - something like level + Charisma bonus + a Feat bonus if you take the "Presence" feat, roll that vs. the target's willpower equivalent and resolve. Other games would require a more specific solution but the concept works in almost any game, and almost every game would be better for it.
*or energy - Champions humor!
** It was harmless college experimentation, I swear!