a friend of mine offered me a c128?

[Voltrom]

What are the possibilities with this thing? Musicwise?

Are there any trackers for it?

I hope someone here already produced with a c64 or 128 and can help me out?

Greets.

[LPChip]

The C64 and C128 has a SID chip allowing to play 3 voices at the same time constructed out of basic waveforms or noise. Modulation is possible. It has filter capabilities, and in the early 90ies, they used the click sound you can hear when switching filters on and off in rapid succession to create a virtual 4th wave channel.

The SID tunes are usually programmed in assembly, but there are some music programs out there. Most are made to just play with some standard sounds, and a few are actually able to create some good tunes. Because the SID chip is so famous, there are some trackers for the PC that will allow you to create SID or PRG files. The PRG files can be played back on a real C64 or C128 by just running the program. The program for the PC is called GoatTracker. Very powerful tracker.

[Saga Musix]

Generally GoatTracker will definitely be a good first step as you can stay within the comfortable PC environment and still get some nice SID sounds, but if you like what you're hearing, it cannot hurt to try the "real" thing - there are plenty of trackers for it, don't expect them to be as user-friendly as OpenMPT, though. Every SID basically sounds different due to cheap and imprecise manufacturing, so working on the real thing can be a unique experience. E.g. the filter on your machine could be much stronger than when you play the same tune in an emulator.
Music-wise, what can be done? Well, check out the High Voltage SID Collection - there are tens of thousands of tunes made on the SID.