rosea grammostola: 
 
 
Hi,

Playing with Radium a bit, so far so good. But how do you Tracker-guys add
chords to your music?


Hi, I don't know whether you are only asking about trackers
in general, or if you are asking about Radium as well (which
may, or may not, be a tracker).

But at least in Radium, you add polyphonic notes by holding
left shift while adding notes.

But to be honest, I've never used this feature myself. I always
use several monophonic tracks instead. It's a nice feature
when importing midi files though.