I have been thinking about Role Playing Games recently... One of the issues I have with the D20 system that a lot of people have had is that everyone wants to know how your warrior can run up.. fight through 30 orcs take 15 blows on his body and be fine the next day... So here are my thoughts:

What about a Energy / Life system... now here me out you people in the back of the crowd:

For a fighter Energy and Life are basically the same thing. You take damage first on your energy, stating that as the battle goes on you get tired so an example--
(Wolf Fighter level 5, high strength and con, Energy 45, Life 16)
(Orc, Energy 16, Life 8)
-Wolf swings his longsword at the orc. Before rolling to hit etc he takes 2 energy points off.
-He hits and with his heightened strength he deals 14 points of damage to the orc, this knocks the orc down to 2 energy and 8 life.
-The orc swings back at Wolf, takes 3 energy points off his total based on the fact that he is using a heavier weapon (Two handed Axe), this knocks the orcs energy down to below 0, first off from now on he will be taking damage into his life points, second off he will be dealing lesser damage due to his wearied state unless he has feats to counteract that (Rage, etc)
-The orc hits but it is a wounding blow (special type of hit, requiring skills or luck of the dice), it doesn't deal more damage that normal but goes straight against Wolfs life total in addition to his energy total. The orc deals 8 damage, Wolf is now at 35 Energy and 8 Life. Normally he wouldn't have taken any damage from the blow except because of the critical strike.

Energy would recuperate with just resting probably 10 points per hour for sitting / eating / drinking, 5 points per hour for non streneous activities.
Life recuperates through extended time or healing.

How the process would work for magic wielders. You would spend energy points to work magic, the amount of energy you spend would directly effect how the spells works. I would go more for a general spell system where you don't necessarily have specific spells, but if you use a specific spell you get more bang for the buck. A priest could cast a fireball in this instance but since it would be against his nature would never be able to learn the spell unlike a wizard and could cost more energy. After a magic user ran out of energy they could continue casting spells into their life total. This would recuperate at a higher speed than normal wounds but slower than energy, but it could still kill you if you overstretched your bounds.

I also thought of armor adding onto a temporary life total and subtracting from the energy total (probably a lot more adding than subtracting)..

Something like:
Full Plate Armor +65Life -20Energy +8 Defense
Leather Armor +10Life 0Energy +2 Defense

It gives lighter armor some benefit but wearing the heavy armor major benefits and negatives, it would also increase the amount of energy lost in fighting / general actions. Climbing a mountain in full plate armor is going to hurt.

Thoughts? Very rough but just something I was thinking about this morning.