I'm not going to go through my entire history, just going to report what I've tried recently. and it's TL;DR already! Quantiloop on the iPad - worked pretty well, but excessively complex and did not sync well with a couple drum machine programs I tried. Also my iPad is usually over on the exercise bike so I can watch Netflix (reminds me I gotta go burn off some Thanksgiving poundage). I got the iPad from work but supposing I bought it myself, I could get a heck of a looper for that amount of money. Thought about getting an E-H 720 or 22500, just for those times when I need something and my project du jour is in pieces. It happens more often than I'd like to admit. I may still get a 720 for those times. 22500 has two loops at once, bank up/down via external switch, starting to seem attactive, BUT... not yet. I got some stuff going in Ableton Live with their "looper" effect but still they expect you to record to a click and have the time signature known ahead of time, which isn't always the case. Sometimes I come up with an off-kilter riff and just want to record it ASAP and figure out the time sig later. Sometimes they even come out as 4/4! I am building up my latest pop hit in Live. I think it's pretty cool. I had tried SooperLooper on an Ubuntu Studio PC and that was getting closer, because I can just record a loop free form and then force additional loops on top of that which are in sync. I think the main issue there is that my computer desk is in a corner, my guitar rig is right behind my chair, and I prefer to face the guitar rig when playing rather than the computer desk. Then I got this wild hair to try SooperLooper on a Raspberry Pi. There's some indication that people have done this. I just went with the latest Raspbian Buster, which already has a bunch of music things in the repository such as SooperLooper. The SL UI is pretty cluttered and has a lot of things that I rarely use, such as 1/2, 2x, insert, replace, etc. so I got the source code and went about trying to reorganize all the onscreen bits. Took longer than I wanted but I think I have a reasonable grasp of how that works now. I'm using a Raspberry Pi 3B in a case with a 7" LCD/touchscreen and it sits on top of my rack box which is the ideal location. Using that with a Macmillen softstep for MIDI control, and a small mouse and keyboard when needed. With the UI changes I made, I can get 3 mono or stereo looper tracks on screen and the Softstep can record/play/overdub/clear for each track with just one button per track so I have 7 other buttons for per-track mute, or global pause, or whatever, I haven't actually figured that out yet. The biggest problem I'm having is little pops and glitches in the audio. I've got the latency dialed down pretty tight because it's unusable otherwise. I've gone through some tutorials for optimizing Pi for audio. Some of the HW design is antithetical for audio work, e.g. ethernet shares something with USB. Also, I want to keep the Pi on the network so a) I can use my regular computer with VNC or SSH for programming, etc. and b) with Samba on the Pi, then the WAV file folder just shows up on my Windows PC and I can use that directly rather than needing to use an application. Next up I am learning what it takes to compile a real time kernel for the Pi. That looks "not easy" but I will just have to sit down and try it over a number of days. I also ordered a Tinkerboard which is same form factor as the Pi, but about 2x the horsepower, or so they say.