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.
Links (FYI, clap is always easier than VST, so prefer it; you may have to enable it in settings or something though):
You can of course also use external stuff like Pure Data and Orca through MIDI, OSC, UDP, or even loopback.