Hmmmm, I don’t really use all that many, at least not that I can think of off the top of my head. I don’t find that games are broken enough to warrant them most of the time and if they are, I don’t play them.
A couple that spring to mind are-
D&D- Wizards can’t wear armour. This isn’t for any reason other than I started playing D&D in 2nd ed and Wizards couldn’t wear armour in that edition. In my mind it makes no sense for wizards to wear armour and so I tend to houserule that they can’t, it’s that simple.
XP- I tend to keep the party on an even playing field with XP, whether they can make a session or not. I never used to work this way but as I grew older and my players grew older life started getting in the way ,people couldn’t make games through no fault of their own and penalising them because of it seemed a little unfair. So, in my games, players tend to sit on the same XP.
Plot Points- My favourite of the lot I think. I’m basically of the opinion that every single game needs some version of plot points. What do I mean by this? Well plot points are intangible points that are not connected to XP or anything like that (although they can be, like in Numenera) and can be used by the DM to drive the story in a certain way by dictating something that a character does, usually in line with their personality. It allows the DM to say things like “You don’t hear your friend being attacked because you are distracted by the person flirting with you”, which just opens up story options and gives the player a plot point.
Players can then spend plot points to dictate story based events or change the plot a little in their favour, with DM approval. So if a player has a plot point and is in prison he could ask the DM “Can I spend a plot point and say that the guards didn’t find a lockpick in my shoe”? If the DM’s cool with it, it happens and the story moves on. Plot points allow collaborative story telling on a level that normal games just don’t.
I have to give huge amounts of credit to FATE for introducing me to using plot points in this way, as its use of aspects and tagging them for benefits is an absolute game changer.