As sibling comment notes, you can switch between WMs at runtime, you just have to not exec the wm from xinitrc. Instead, you run a terminal emulator or whatever as the first X client, and then from there run the window manager like a normal program. I mean, I'm sure there are nicer ways to do it, but that worked for me.

Alternatively, if you want to run multiple at once, you can run Xephyr, which nests X sessions, and then you just run whatever clients you want in each child X server, including the window manager.

Any way of achieving this without opening a terminal? Presumably closing the terminal kills the WM?

Sorry; I know it can be done because I've seen systems (live CDs?) do it (they even had a nice menu where you could click the wm you wanted IIRC), but I never learned details.

Yeah, I’m guessing running startx without one, then executing one on top, that way X doesn’t cascade terminate when the session ends or something. This is something that would improve workflow in situations where I want to use a floating wm, without terminating all windows.

CTRL+ALT plus function keys to go to a console tty.

You can switch WMs on the fly, just terminate one and start another. X server and applications survive restarting/switching WMs.

What command do you use for this? kill $pid && openbox doesn’t work for me.

1: Not sure what you mean by that

2: It's possible. Some things support this for example compiz can be used to replace the running wm in place via compiz --replace.

Qubes is the best for managing VMs, it’s known as a security minded distro but it’s really the most well thought out VM manager I’ve seen. VMs are so well integrated.

WM =/= VM, in case you're curious about downvotes.