@ljwrites
I got a license years ago as part of a #MacHeist bundle. Not sure if that version would still work on the recent versions of #macOS though...
#SpaceSniffer usually is the go-to alternative for #Windows for me: http://www.uderzo.it/main_products/space_sniffer/
I bet #Linux has a GUI one too, though since I've discovered #ncdu I tend to stick to that CLI one. :) (Especially since I primarily use Linux without a WM/DE).