Just curious what you guys think. Maybe it's something that you homebrewed yourself. Maybe it's just something you happen to come across while browsing the web that looked intriguing. I'd be more interested in hearing about RPGs that actually invented their own mechanics and rule-sets as opposed to the, probably, millions of d20 based knock-offs out there. Some of those might still be worth mentioning if they are really unique in some way.
Well, the best homebrew I had was actually based on d20, but significantly different because of the themes that were present. If you've ever played the Milton Bradley electronic board game, Dark Tower, the campaign was based entirely on that.
Fighting rules pretty much remained the same, although I did play with an idea of a 20 card deck for each class to use in combat rather than a 20-sided die, but later changed my mind. I did have to change the mechanics of magic quite a bit, since in the world of the Dark Tower, magic had basically died. (It's a post-magical-apocalypse world.)
Sorcerers had little access to spells, Wizards and Druids had basically been killed off. (The only way a sorcerer could have a spell was to use a feat for Spell Knowledge), or to possess some item of faery creation. A faery orb for example allowed its user (if a sorcerer or Cleric of the Arcane Collective), to cast light at will, and detect magic three times per day, but other than items like that, no spellcaster had access to cantrips.
Divine magic was also affected. Most of the divine agencies were seperated from the lands by the rising of the Dark Tower, so clerics had to continually make Meditation (a new skill) and concentration checks to have access to and cast spells.
Paladins and Rangers had slightly different abilities to reflect a campaign that was high fantasy yet low in magic access. I am still in love with this campaign, and hoped that I could publish it at one time. However, with the legal problems surrounding the original board game it was based on, that is probably a virtual impossibility.
I have a couple that I've tinkered with before, but the only one that got to a testable state was Totte Gotter.
I put in a couple of interesting ideas with the system - it used a 3x3 matrix for attributes from category (Physical, Mental, and Spirit) and focus (Attack, Defense, and Durability). Skills could be combined on a single skill check as long as it makes sense and all skills use the same two attributes, and multiple checks can be made in a single action by taking an ever-increasing penalty.
Skills were user defined, and cost a number of character points depending on the breadth of the skill and how likely the skill was to come up. Combat was a matter of taking out your opponents abilities before they took out yours.
Never did finish fleshing the system out, but the group I played it with did seem to enjoy the system when I did a test run of it.