Here is an idea I have been turning over in my mind lately.
The inspiration came from a rule used by an old gaming buddy of mine from my college years, one with whom I have occasional online chats about D&D. He is currently DMing a long running campaign of heavily house-ruled Cyclopedia D&D. One of his many rules modifications is that magic-users, once per level, can perform a "Great Work." The Great Work is a magical effect that is not a spell, and the power level of said effect is usually far beyond what the magic-user is normally capable of, though still determined by level. For instance, a low level magic-user might be able to redirect the course of a river or wither a field of crops, while a high level magic-user might be able to build a flying castle or cause a plauge. I'm not sure if unused Great Works carry from level to level... in fact, beyond the "once per level" rule, I don't have many of the specifics, but it gave me an idea...
So far I can think of no better title than Feats, though more along the lines of Feats of Strength or Feats of Skill, rather than the d20 mechanic. Basically, what it entails is that once per experience level, a player may do something quite impressive. A fighter might choose to perform a Feat of Strength, where, for one particular task, he is treated as having the strength of an ogre, or, if he is that strong already, a hill giant. The fighter might instead perform a Feat of Accuracy where he shoots out the eye of a dragon or makes a one-in-a-million shot. A cleric might perform a Feat of Faith where he heals all the dying on a battlefield or cleanses a town of the plague. I haven't hammered down any specifics; for now this is just an idea. For some reason, I can see this implemented in a basic D&D game, but this isn't something I'd include in my current AD&D campaign. A few of the parameters I am considering:
1. The feats one can perform (strength, archery/accuracy, skill, magic, faith, thievery, etc.) are limited by character class.
2. You can only do this once per experience level, and unused feats do not carry over.
3. The scope of the feat is determined somewhat by experience level... a small time 1st level character's Feat of Strength isn't going to make it into bard songs quite the way a 10th level lord's is.
4. Optionally, the character might have to save vs. some consequence... perhaps a great feat of ogre strength requires a successful save vs. death to avoid perishing from the strain. (Upon the deed's completion, of course)
5. Level draining does not "reset" a feat. (Though you may recall that energy drain takes away Hit Die, not levels, as described in an older post.)
6. Since this is presently imagined for basic D&D, I don't have to answer the multi-class question just yet.
7. Option- For a human-centric campaign, consider demi-humans only getting a feat ad odd numbered levels. (Or some other arbitrary limitation) If I do include Feats in a future game, I most likely will not implement this... it's just food for thought.
Some possible examples of Feats:
1. Inflictt a mighty blow that instantly kills a greater foe. For those DMs uncomfortable with this, consider maximum damage or a damage multiplier or some such.
2. Damage a creature that ordinarily cannot be damaged by the weapon you wield. (Slay a gargoyle with a normal weapon, for instance)
3. Automatically pass a saving throw, or perhaps ignore the results of a failed saving throw
4. Temporarily gain extra hit points, which vanish after a great and terrible battle. (Yes, you can die when they go away) Alternately, resist dying of lost hit points until some immediate foe or deed is conquered. (Think Beowulf and the dragon)
5. Temporarily gain the strength of an ogre to complete a given task. (Smash open the gates of an enemy fort, lift a fallen tree blocking a river, etc.)
6. Cast a spell beyond one's level, or perform a feat of magic not found among the spell lists.
7. Automatically succeed at a thief skill roll, even under conditions that would normally make it impossible. At high levels, perhaps gain 99% in all thief skills for 1d4 rounds or to complete an immediate task.
Well, that's the skeleton of the idea. Any thoughts? This is something I'm interesting in tinkering with further. It might be a nice, happy medium between totally mundane PCs and the more cinematic hero approach adopted by 4e.