It shows current bundles moving through wires, and portraying the interaction between components.
It comes with a library of circuits.
You can construct your own circuits. You can save them to disk and read them again.
This link will open the website and load a bandpass filter using an LC tank circuit. It will then run immediately on your computer. (Click Allow to load the Java applet.)
Falstad's has its limitations (although this is true of every simulator).
There are numerous simulators which get a favorable report at this message board. Many are in the Spice family, and have features which Falstad's does not.
Hey I know you are looking for a free software but here is a good simulator for cheap. Its called circuitlogix and it only costs $39 (from memory) for a lifetime and its very useful. Its a much simpler interface than the multisim and its a one window application. So have a look at it. Its got a free trial for 15 days or so.