While writing [this answer](https://quantumcomputing.stackexchange.com/a/6196) I realized it would be really helpful if I could show the OP a video or .gif of how qubit states in Bloch spheres transform under certain unitary operations. I googled up a bit and could find only these two simulators:

* [Bloch Sphere Simulation (Stephen Shary and Dr. Marc Cahay)](https://eecs.ceas.uc.edu/~cahaymm/blochsphere/index.html)
* [Wolfram Demonstration Project: Qubits on the Poincaré (Bloch) Sphere](http://demonstrations.wolfram.com/QubitsOnThePoincareBlochSphere/)

Both involve some messy software installations and I don't really want to do that. The second one apparently doesn't even allow the user to input arbitrary 2×2 operators!

**P.S**: It would be great if [Craig Gidney](https://quantumcomputing.stackexchange.com/users/119/craig-gidney?tab=profile) could add a full-fledged Bloch sphere simulator within [Quirk](https://algassert.com/quirk) at some point (ideally, by making the already existing Bloch sphere views of the qubit states clickable and enlargeable). :)