FREE microtonal VSTi

Its in development but sounds very promising

http://zynaddsubfx.sourceforge.net/

# Realtime synth
# Polyphonic synth (allows playing more than one note at once)
# Mutlitimbral synth (allows playing more than one instrument at once)
# Microtonal capabilities with any scale, up to 128 notes per octave, and key mapping