Psycle is a free, open source music creation program for Windows, similar to Buzz, but with a somewhat more usable interface.

Psycle has two main screens - the Machine view and the Patterns view. To create a song, you create Machines, which can be either Generators, which generate signals, or Effects, which process signals. You then create Patterns, which tell the Machines what to do.

Psycle comes with many different Machines. Most of the Generators are designed for synth-type sounds, and they range from the simple (for instance, the DrumSynth, which generates a simple 808-like bass drum sound) to the alarmingly complex (the control panel for the Pooplog FM Laboratory has 88 adjustable parameters.) There is also a Sampler machine, which can take external sound files and play them back at different pitches and speeds, similar to a traditional tracker.

Most of the Machines, save a few basic effect plugins, come in the form of external dlls which are stored in the Psycle directory. Psycle supports VST and VSTi as well as its own internal plugin format, which allows access to a bewildering variety of synths, samplers and sound manglers, many of which are available for free download online.

Once you've got your Machines set up, you switch to the Pattern view, which takes the form of a modified tracker. If you've ever used Impulse Tracker, FastTracker or any of their derivatives (ModPlug etc) you should be relatively comfortable here. Notes are entered on a spreadsheet-like grid using either the PC keyboard or an external MIDI keyboard.

In terms of interface design, Psycle is attractive and reasonably usable. It has a few annoying interface quirks (the pattern sequence editor is particularly hard to use) and it suffers from a lack of presets for the machines, but if you need a free tracker that supports VSTi this is a pretty good choice.

Alternatively, you could try the commercial tracker Renoise, which is much prettier, relatively cheap ($45 USD) but which I found fiddly and annoying to use; FruityLoops ($49 - $99 USD) which is also very attractive and more powerful than Renoise, but which is again fiddly and annoying; or Buzz, which is free but doesn't support VSTi and which I found rather ugly and had trouble learning to use.