Vadim Zavalishin (DrSync) and Native Instruments have officially made SynC Modular freeware.

SynC Modular is a modular software synthesizer VST instrument plug-in for Windows.

Features:

• High Performance: The performance of SynC Modular compares to the performance of non-modular software synths. This means higher polyphony and/or patch complexity.
• Flexibility: SynC Modular allows you to create your own oscillators and filters (using Z-1 modules of course).
• Multi-timbrality: SynC Modular allows you to have as many as 16 parts playing together. Each part can select a different instrument in realtime by receiving a MIDI program change.