@lawrencegripper @chiser99 I'm guessing here but I don't think it's really an "app", I believe it's more like they built a new desktop environment where Steam is both the launcher and the window manager. No need to reboot to enter or leave it, it's just like switching between say GNOME and KDE on a regular distro. (So it's not running KDE "behind" Steam.) This is just a guess, but it seems a very sensible way to do it.