The programs on this page should help you if you're interested in either listening to or making tracker music. However, this is only a small fraction of the programs out there. For a much more useful and complete list, check out Maz's Sound Tools!
 

MODPlug Player
In my opinion, this is the best all-around program for playing files of any tracking format. I thinking it's missing support for some of the most extremely new formats, but you'll find very few songs in those formats right now anyway. In the meantime, this program will come the closest to 100% accuracy on playing ITs and XMs you'll find anywhere except in the native tracking programs themselves. And because of its accuracy, wide support, Windows-base, and customizable playback settings, MODPlug is great for playing MODs in the background while you do something else on your computer. Heck, I'm doing that right now, as I write this. :)

WinAmp
WinAmp is excellent for playing MP3s, and it can also play tracked music. But for tracker music, it's not nearly as accurate as the MODPlug Player. So, here's my suggestion: if your music collection features lots of MP3s AND tracked music and you want to be able to play both without jumping from program to program, WinAmp is good enough. But if all you play is tracked music, forget WinAmp: grab MODPlug Player instead.
 

Impulse Tracker
Plays MODs, S3Ms, XMs, and ITs. Writes S3Ms and ITs. It looks very much like Scream Tracker and has all of the same features, but it also has some more advanced features of its own. If you've used Scream Tracker for writing songs for a while and you want to take your music to the next level, this is the program for you! This is THE latest version of Impulse Tracker, so it can play any compressed IT files you may come across that won't play on older versions of Impulse Tracker. Even better, the program now supports MMX, along with Direct-X drivers, meaning that you can run this just fine from a DOS shell in Windows 95 now without trying to coax your normal sound drivers into cooperating. (Note: If you run into any memory problems, READ THE IT.TXT FILE. It will tell you how to fix the problem. Heck, even if you don't have memory issues, read the IT.TXT file anyway. ;] )

Fast Tracker
Plays MODs, S3Ms, and XMs. Writes XMs. Not quite as advanced as Impulse Tracker, but make no mistake about it: this is a VERY high-quality program that puts out some excellent music. Many trackers swear this program is easier to use than Impulse Tracker, although I beg to differ. ;) Choosing between FT2 or IT is a lot like choosing between Coke and Pepsi, or IBM and Macintosh. But I happen to prefer Impulse Tracker. ;)