"Single-Application Mode" in Debian, is it possible?
 

There's this feature in MacOSX called "Single application mode", that makes it so only one window shows up. I was looking at ratpoison, but that doesn't allow the panel to run. What I would want is for my KDE-Dock and the menubar to stay, but only one "main" app loads at a time [the rest are "hidden", not minimized, either]. is this possible?

Search for "KDE kiosk mode"

I don't see an option in that for having only one app showing at a time, it just shows things to "lock down" the system. Is there a set of commands to use it?

What I mean is, for example, if KMail is open, and I want to switch to Amarok, I press Alt-Tab, and KMail vanishes from the screen as Amarok appears. However, KMail is still running in the background. [If this makes sense]

Sorry, I haven't actually used it, I found it a couple of years back when I was scoping a project but didn't get a chance to look at it any further or implement it. When I read your post I interpreted it to mean you were looking for something like Citrix published apps, but I realise now that was incorrect...