For me, it was perhaps simple-scan, a very simple and efficient GUI to scan documents. I used it with my Brother printer / scanner and it works like a charm. Especially since I do not scan stuff often, so a program with more complex UI would have the effect that I forget how to use it until the next time.
Mixx is a cool free dj software, didn’t expect davinci resolve to have an official version, stremio also I didn’t think would have an app for whatever reason. I like inkscape for vector art, didn’t realize it was a thing til I swapped to linux. I use software and apps more in general because it’s stuff I’ve installed and its not hidden by bloat, even if there is more windows stuff out there, its way easier to discover actual useful software using linux through linux appstores compared to windows.