I wrote a couple of TSR programs too, nothing too advanced, but it was a fun time to be learning and experimenting. I suspect the most useful thing I wrote was

I wrote a couple of TSR programs too, nothing too advanced, but it was a fun time to be learning and experimenting. I suspect the most useful thing I wrote was a simple "undeleter" program, for recovering deleted files from floppies and drives. Unmarking the FAT-entry as deleted, then chasing blocks to reassemble the file.