This is a very warm and natural sounding tube tremolo/overdrive.
With vol, gain, speed and depth controls you can get a variety of sounds out of one box. When depth is set to zero you can use it as a normal booster/overdrive pedal with vol&gain controls. Turn depth clockwise to add some smooth tremolo and turn gain a bit down to clean it up. Or just leave the gain up there since tremolo + overdrive sounds very good :) Speed controls the rate of tremolo (flapping of wings).
Custom made for Gabe @ kitaramaailma.com (Check out his website, good info in there!)
Some sounds samples:
Recording chain: Telecaster->Hummingbird->Mixer->Soundcard->Cubase Amp simulator. First you hear clean sound, then tremolo. Overdrive section is not covered in these clips, going to make some new clips soon!