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 believe it was the Linux counterpart of XSplit, the “other” streaming software that was very popular in the early days of streaming. Before that we had to use some very elaborate setups.