Something from a capsule review in Space Gamer has stuck with me through the years, a comment that there's more than one reason to buy a new game. Sometimes it's not going to replace your favourite, or even get played at all, but it may well provide useful material nonetheless.
D&D 5th edition is certainly not the first appearance of the Advantage / Disadvantage mechanic, where instead of a single die you roll two dice and take the better or worse result depending on whether you are at an advantage or a disadvantage, but it's probably the most prominent. It's a clever, useful and extremely easy to steal rule, adaptable to many other systems; and I can see myself duly pinching it and trying it out in different games.
What rules have you successfully ported from one game to another? Is there a particular reason why they fit? or do you use them despite a slightly clunky connection with your preferred mechanics? Let's see some suggestions so everyone can get stealing