Fate Points
As mentioned on EN World, players can get fate points by: So that could be up to 3 fate points per session. The points can then be used to reroll one d20 (skill check, attack roll, save, etc) or one d100 (stabilization) at any time. The player has to take the second roll, so they probably only want to do this if they've failed on the first roll.
Using 3d6 vs 1d20
Some people may prefer to roll 3d6 instead of 1d20. This reduces randomness a fair amount, so if you want to maintain critical hit averages, then you need to use 16-18 instead of 20, 15-18 instead of 19-20, and 14-18 instead of 18-20, etc. On the other hand, I'd suggest keeping it at 18, 17-18, and 16-18, to keep critical hits down, since randomness tends to favor monsters. Any d20 roll should be able to be converted to a 3d6 roll, which will have a much higher likelihood of middle values than a regular d20 roll (10-11 is 25% instead of 10%). The average value doesn't change, and the range is very similar, so it should be safe to switch to 3d6 instead of 1d20 at any time.