So I was planning a project, when the arduino I was using ran out of pins. I had no multiplexer laying around. Nor had I any other ready made solutions. But when I browsed my "chip collection", I found a handful of 4017 decade counters. I used them in a step sequencer together with a 555 as clock, when I build a drone synth some time ago.
I thought: If I timed the clock signal, maybe I could send the outputs of the counter through the switches in the project, and as long as they where used as pull down, it might work.There's probably more drawbacks than I can imagine, but it worked for the user input buttons that I needed.
Source code and diagram of the demo in the video can be found on the linked github page.