I mean a system that could be used for either.
Let me abstract it for you. I set up a thief character with low strength stats, high agility/dexterity stats, good intellectual stats. I give her skills in picking locks and pockets, in hiding and getting lost in a crowd, and in running.
You set up a big barbarian with great strength and health, decent agility/dex, and tolerable presence. You give him great skills in brawling with some concentration in a few weapons like spear and axe, some intimidation, and some observation. You buy him leathers and an axe. We each set ourselves interactive, which means vulnerable to others' skills; this can be turned off for purer role-playing, but loses the faster route to increase scores through use.
You walk him into a bar and buy a drink. I walk by and try to pick your pocket.
This triggers several evaluations. Do I succeed? (My skill, modified by your armor.) Do you notice? (Your observation skill vs my pocket picking.)
1) I get something (only stuff you mark as ok, or fabricated from a pool of "karma" used for this sort of thing), and you don't notice - I walk away richer.
2) I get something, but you notice. Now I can run for it and have subsequent rolls to see if you can lay hands on me, or if I can get lost in the crowd. Complex, would require some HUDs and/or creative interfaces, but those time delays become part of the game.
3) I fail to get anything, but you don't notice. I can try again or wander off.
4) I fail to getanything, but you DO notice. see #2.
In every case, both players have had at least one opportunity each to roll using a skill. Every roll includes a chance to increase that skill. Any increase pays "karma" to both players, which can be used to improve rolls, spent to increase skills, or tapped to provide results, such as creating the beads I stole from your pocket.
Yes, the options would need to be considered in advance. Entire encounters could be prewritten as standard events, and players could list their preferred behaviors in standard situations. Long way to go? yes, but that's the point.
In cases of actual combat, two guys duking it out, then each has a chance to hit the other, but can shift points to defense to make it harder to be hit, at the cost of making it harder to make a hit. Get your skill high enough, you dosdge like Spider Man and swing like Captain America (and yes, it would work just fine for superhero sims). Soft armor increases your dodge, hard armor also counts against damage delivered, though reduces your mobility. Weapons can increase your effective skill and certainly change the way damage is applied.
Damage is mostly fatigue, wearing you down, but depending on the attributes of the wepon would also include a loss of real health, of strength, of agility... Stuff a computer can randomly apply according to rules. "Death" is character inactivity, but depending on local implementation could be a simple teleport home, or a more elaborate collapse until priests or medics can revive the avatar.
What I'm talking about is a system and the tools to implement it. A standard, and some examples. I'd like to build a Roman style arena, and start with bare fisticuffs until we can get more elaborate armor and weapons implemented.
Wow. Long, rambling response. Thanks for the question, though.