The Wikipedia IFTTT recipes are cool. The technical guide explains the triggers they use, maybe the hub can explain the implementation of the triggers: roughly, a Flask web service that makes action=featuredfeed API calls, DB queries, and caches recent changes to look for changes).
Related/instead: spage has started API:Showing interesting content for T108661: Showcase/inspire: showing interesting content using FeaturedFeeds which talks about the featuredfeed API module on WMF wikis and goes into some detail on ifttt recipes using it.