Still tinkering with CP/M tools these days.
DOS has CP/M at its roots, so does MSX-DOS. Which means I can be dropped into its command prompt and have a decent idea how to move around and get basic stuff done. But then getting into nitty-gritty details feels like a rabbit hole: version 2 vs. 3, derivative systems, alternative command interpreters and batch processors, CCP, ZCPR, Z-System, MP/M... I get lost easily.
So yeah, quite the learning process.