Caustic is a music creation tool inspired by rack-mount synthesizers / samplers rigs.
Windows Desktop version is free, full version, but no support.
http://www.singlecellsoftware.com/caustic---
Bristol Audio Emulations
Bristol is an emulation package for a number of different 'classic' synthesisers including additive and subtractive and a few organs. The application consists of the engine, which is called bristol, and its own GUI library called brighton that represents all the emulations.
Bristol is only available on your favorite Linux platform. It will not work on any windows release, nor will compile on any version of BSD without considerable effort - on your part.
Bristol is free.
http://bristol.sourceforge.net/