[sagas-of-the-icelanders] or [tremulus] or [apocalypse-world] or [dungeon-world] or [the-sprawl] or [powered-by-the-apocalypse] or [monsterhearts] or [monster-of-the-week] is:question should do the trick. (Results of that search here.)
[foo] in the search bar specifies a tag; "or" works as you might presume
is:question limits the return to question-posts.
That list of tags was generated from this SEDE query, helpfully created by @Miniman. It only finds tags whose description mention being powered by the apocalypse. (If you find some tags missing this in their description, please edit it in! It'll improve the site and your ability to find them... win-win!)