FoolsWin: A very simple program which writes a derogatory message about M$ Windoze if somebody (eg. a PC-owning friend) tries to type "win" at a shell prompt. Coded in asm although it is only like two lines in C. Never mind.
GetMouseDOS: Very short program which returns WARN (5) if the left mouse button is pressed when it executes. Can be handy in a startup-script to conditionally execute something. Although to be honest, if you couldn't code this yourself....
QWait: You know how you've got a "wait" command in AmigaDOS? Well it will only wait for times to the nearest second. QWait takes a numeric argument and waits that many 50ths of a second. Handy for, say, a half-second wait. "QWait 25".
AnyMem Patch: Probably not much use nowadays. Some old programs used to specifically ask for FASTRAM (set MEMF_FAST flag during allocation). There is, with only very few exceptions, no reason why the average program needs to do this. This simple patch can be run at startup and then any requests for Fast Ram will be translated into "any" ram. I originally wrote this to make Pixel3D Pro work on a chipram-only machine.