Iain Sharp, maker of the popular and addictive LushOne synth – and other kits – also has this Circuit Simulator online. The simulator is based on Paul Falstad’s simulator, however his being Java-based, will require a plugin, whereas Sharp’s version is built using HTML5. Think of these like animated Fritzing circuits, with a slew of pre-built circuits and components available for tinkering with:
To turn a switch on or off, just click on it. If you move the mouse over any component of the circuit, you will see a short description of that component and its current state in the lower right corner of the window. To modify a component, move the mouse over it, click the right mouse button (or control-click if you have a Mac) and select “Edit”. You can also access the edit function by double-clicking on a component.