Another good one is http://www.falstad.com/circuit. I remember using this quite a bit to double check homework.

When I was at NI I helped build https://www.multisim.com which is powered by a full SPICE simulator.

Yep! It was inspired by all these simulators :)

I believe that's quite the unfair comparison.

Even if the components model aren't very sophisticated, everycircuit can do full analog simulations.

If you use chrome, you can run everycircuit in-browser, then try this example: http://everycircuit.com/circuit/4709435733180416/infinite-no....

Circuitverse, as far as I can tell is just a logic simulator, which - from reading the comments - doesn't handle feedback loops.