if u want a free rewire host, download reaper.
open reaper, add a new channel, right click the channel and 'add a virtual instrument to channel' in the window that pops up click vsti's or dxi and open massive.
then do the same, but instead of clicking the vsti or dxi tab, go to rewire, and chose reason. reason should open automatically in the background, and use the three softwares together easily.
just make sure in reaper you chose the bpm of the track your making, otherwise it makes reason and massive sync to 120bpm (reapers default bpm, you can change this just below the horizontal midi timeline scrollbar).