Hey, if you are willing, I would like to hear more about these!
1) Allowing a free tag on an aspect to be a compel instead of an invoke.
2) Limiting non-free aspect invocations to one per context (personal, scene, zone, etc).
3) The entire social combat system, which I'm going to use for a trial in my Dresden Files game.
#1 is simple, if you do a Declaration, Maneuver, or inflict a Consequence that gives you a free tag on the attendant aspect, you can use it to compel the subject instead of just getting the invoke bonuses. I like this especially for Consequences, because it allows for situations like using a free tag to compel someone to stay put after you put a "Broken Leg" consequence on them.
#2 just disallows invoking multiple aspects in the same context for the same roll. So, you can't invoke two of your personal aspect but you could invoke one of your personal aspects, a scene aspect, and an aspect on the zone. This helps to keep potential roll results down.
#3 is a bit involved to explain at length, but in a nutshell it involves using abstract zone maps and often abstract participants to handle conflict resolution. Players on the board can be individual characters, groups of characters (with composite scores), or abstract concepts or variables.
So, for example, in the trial I am running there is a line of six zones: three guilty, three undecided, and three innocent. There are three participants on the map: prosecutor, defender, and jury. Each stage of the trial is an exchange (opening statement, each witness, closing statement) during which the lawyers affect the position of the jury, trying to "move" them in to the position they want. The final position will determine the verdict and how long it takes to render (all the way at the guilty end will get you a guilt verdict in an afternoon, in the first innocent box will get you a not guilty verdict in a few days). I'm keeping it simple because this is my first go at it, but I could also have the witnesses on the map, with their guilt or innocence showing the jury's opinion of their trustworthiness.
Another example I loved was on one of the Diaspora boards and involved a target-shaped map with KILL at the center and FOILED in the outer ring to do an assassination. The target and assassin are on the map as are the variables Secrecy, Means, and Opportunity. Each participants wants to get the other as well as two of the variables into the appropriate position. If the assassin, secrecy, and means are in FOILED, the assassin's cover is blown and his tools are discovered or captured. If the target, means, and opportunity are in KILL, the target is taken out, but not secretly (the assassin saw their chance and took it, damn subtlty!).
Basically, the neat thing is that you can map anything with it and, if you do it right, will have a story to tell from the final positions on the map and the time increments are up to you, so you could map a political campaign or other long timescale occurrence as easily as a seduction or conversation over drinks.