I've been running Slack for a few years now, and up until recently I've always used Gnome with Enlightenment. Now that I'm running Slack on an older laptop I've discovered Fluxbox in my quest for a window manager that isn't a memory hog. In my searching I've seen some screens of people with terminal output superimposed over their backgrounds. I've even seen what looked like working command lines on the desktop (no they weren't just transparent terminal emulators, and yes I do know that `aterm -tr -trsb` will give me a transparent terminal window.)
is a link that is very close to what I am talking about.