MadTracker is a sample-based music composition tool and version 2.5 is currently in beta testing with full support for the VST specification and ReWire, plus it features a built in IRC client!

"MadTracker doesn't have a pianoroll. Nor a matrix. You don't need them. Forget about conventions."

Features:

• Intuitive window-based interface.
• Pattern-based sequencer.
• Integrated sampler.
• VST 2 support (supports multi-timbral instruments and graphical automation).
• ReWire support (as synth).
• Built-in chat (you won't be alone anymore when you seek inspiration or help).

MadTracker can be used freely without any nag screen or limitations but ReWire and the ability to mixdown a song to WAV are only available in the Pro version which costs 40 EUR.