In Index Card RPG, all checks roll "damage", which is called effort. You need to roll 20 charisma effort to convince this guard. You need to roll 10 strength effort to bust open this old door. You need to roll 20 weapon damage effort to kill this monster.
In Index Card RPG, the entire room has a DC called a Target, instead of 15 different DCs and ACs in one room.
In Index Card RPG, initiative is just "Who goes first?" then you go in clockwise table order.
In Index Card RPG, roll a timer 1d4. Something happen in 1d4 rounds. Keeps the action going without lulls while maintaining suspense.
In Dungeon Crawl Classics (and other systems), you can keep using spells until you fail. Then you forget it for the rest of the day, or it gets harder to cast more spells.
In Far Away Land, you collaboratively create the world map before the first session.
In Dungeon World (and other systems) you roll 2d6 to resolve instead of a d20.
10+: You do it
7-9: You do it, but at a price.
6-: The GM says what happens, mark XP
In Dungeon World's, Bonds creates party character relationships with a fill-in-the-blank part of the character sheet, like "____ killed my brother" or "____ trusted me with a secret". You get experience points when you fulfill or use a bond, and can create more as your character grows.
In OSR games, you gain XP from treasure, not killing things. Sneak past, convince, steal, to get treasure.
In 13th Age you have an escalation die/counter/timer which increases +1 each round, and various game effects and character abilities take this into account. Things get more heated, so the mechanics should reflect that.
In 13th Age, Icons are major background character forces which impact dice rolls having to do with the Icons, plus the story at large. There is also the Background part of your character sheet, which also affects rolls having do do with your history as a character.
In ??? your armor decreases with/in addition to HP, over time.