HTML5 Based Digital Circuit Simulator, For students, hobbyist.
Circuits Cloud is provides online web site, in-browser tools for schematic capture and circuit simulation. These tools allow students, hobbyists, and professional engineers to design and analyze digital systems before ever building a prototype. Online schematic capture lets users easily share and discuss their designs, while online circuit simulation allows for quick design iteration and accelerated learning about logical circuit.

the website :
http://circuits-cloud.com/
Moderator’s Edit:-
Normally, adverts of this sort are forbidden on this forum, but Circuit Cloud has assured us that use of the application is free.