[Falkon1313]

I had one TSR that let you allocate RAM and switch between up to 3 programs. Of course, they had to be small programs due to the 640KB limit. But it was still quite useful in the days before hard drives, to be able to have a couple of utilities (like a text editor) loaded without having to keep swapping floppy disks.

Also wrote a couple of TSRs of my own as a kid learning to program. Sure you could crash the system, as you could with any program, but they were as reliable as anything else.

The only thing special was that you generally didn't want to run two TSRs that naively hooked the same interrupt without chaining properly. But back then we didn't have thousands of mysterious background processes always running in the background. You knew what few programs you had run, so it wasn't really a problem.