I've tried starting a full screen application without a window manager, using xinit,
which works but instead of starting at the top left of the screen the application starts somewhere in the middle of my screen.
I've tried the same using a custom entry in /usr/share/xsessions
and starting that from lightdm instead
of the default ubuntu window manager, but that gives me the same result.
I recently installed a "window manager" (Steam's Big Picture) that crashes on load, effectively preventing me from doing anything. I've thought of two possible solutions: one would be to edit the file that stores the default window manager, and change it back to LXDE; the other (maybe even easier) would be to re-enable password prompt before login, so that I can change the Window manager there.