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.
I cannot recall any specific programs besides a game called Feudal Tactics, but I swear I’ve seen software while looking through EasyFlatpak that surprised me.