Really cool online logic gate simulator:

http://joshblog.net/projects/logic-gate-simulator/Logicly.html

 

Excellent! I tried to build one when I was a teenager, with poor success. Had been playing around with the 500n1 project kit, and it inspired me.

I remember the ones I used to use in college, big and bulky, but it worked. Used a light bulb to show the logic state. I suspect the bulbs were connected to 60Hz instead of DC, because when you clocked them just right they would strobe, slowly turn off, then slowly turn on, as a function of the beat frequency.

 

Great simulator. thanx for link.