Fsyntyhz has released ProgAte, a free MIDI processor/router VSTi, allowing you to control up to 8 synths with one MIDI keyboard.

GETTING STARTED

1) Insert Prog8 between your midi keyboard and the synths to be controlled. In other words, the synths must receive MIDI data strictly from ProgAte’s midi output.
2) Set each synth to corresponding midi channel. Many synths do provide midi channel choise. Alternatively, you may use your host’s midi filters.
3) Setup programs (read sections below)
4) Save your ProgAte’s set as *.fxb for future use

ProgAte is available as freeware on Fsynthz. Check their site for more synths and effects.

More info: ProgAte MIDI processor/router VSTi