Yeah, didgeridoos make one main note that's determined by the length and shape. It's often maligned as a one-note instrument, but that's because most people have never heard one played well. I think of it as more of a percussive instrument that happens to be played with your breath (if you know north Indian music, it's kind of like the tambura and the tablas all in one), and also as klangfarbenmelodie - Schoenberg's term for music that is created through changing timbre rather than changing notes.
ANYWAY! Yeah, when I was first starting out, I figured I had to collect all 12 keys to play with other musicians. You can make slide didgeridoos, but since they have to be smooth and regular, they just don't have the character of more raw instruments. After the initial collecting of keys, then I got into more cultural stuff and the different ways instruments are made in different regions. So I ended up with about 20. And then I moved to Australia not knowing how long I'd be there, so left the original collection behind and started a new one there. Now they're all in one place. My little living room forest.