I have been playing with several logic gate emulators to find one that is a good fit.
- Logic.ly This is my favorite interface for these programs. it is easy to use, and the graphics of a switch and light bulbs help make it clear what these tools are doing. This is not free, it costs $29.99. There is a good on line demo that is free, but students cannot save their work.
- Logic Gate Simulator This one is shareware. Great interface and I love that I can send it home with the students if needed.