It’s got an incredibly ugly interface, and it ain’t Native Instruments FM7 by any stretch, but CuteVST has two things going for it: first, it’s an FM synth that’s open source, and second, it imports Yamaha DX7 sysex data. So think of the ugly interface as geek cred. It’s the real deal: classic 6-operator synthesis, modeling the original Yamaha keyboard. Downloads for Windows available at SourceForge. Thanks, AA!
But, wait, there’s more: CuteVST is a port of Hexter for Linux/LADSPA. Meaning you can download for LADSPA hosts — and probably meaning you can run this on the Mac, if you’re really savvy. I’m just going back to Ableton Operator, thanks.