useful digital simulator, on line.

i havent played with this much yet , but it looks like it could be a good learning tool for students.
if you need some kind of digital similator try this one. im not sure how big a circuit it can handle but has half and full adders, should be able to build the basics of a processor..

https://simulator.io/

very cool site on philips mechanical and electrical engineering kits

http://www.hansotten.com/electronic-kits/ee-series/ee8-ee20-a20/

worth a look, there are lots of useful things here for the experimenter.