Draw inverting rectangles on the screen, no way to quit but to reboot.   I found this on a random mac, named "Mondrian" dated 1986 with no resources to tell you more about it

MouseTrap is an early 1980's programming demo that featured a mouse capture in a square in the center of the screen.  That's all there is to it.  

Mesmer draws colorful sinusoidal function lines on the right half of the screen and then cycles through the colors along those lines. To end the simulation, click the mouse and wait for 10-15 seconds until the cycle is complete.  It will...

Meltdown is a super tiny app (1.9KB!!) that makes your 9" monitor screen melt :) Meltdown is a much cruder and crashier clone of Melt.  

MacFishTank simply puts a bunch of big green fish swimming across the screen while you work.  This RealBasic app is silent. From the author: MacFishTank was devised one day, as a joke by Kris Harris, the overlord of Wild Cat Software. After...