Electro-Harmonix Guitar Synth is an old guitar effect. You plug in the guitar and the box creates a synth sound based on what you're playing.While it has many parameters, it doesn't do oscilations, and as such tends to sound like an auto wah. I have immense respect for Brian May, but the solo in question is most definitely played with this box or alike. I've had that effect box for a while, and am aware of its capabilities. Try any guitar synth effect and judge for yourself, but don't haste into "no effects, just his hands and a weird guitar". I only use a wah and a Marshall most of the time, but I'm trying to develop an ability to recognize other effects when I hear them.