discoDSP has released OPL, a software FM synthesizer plugin based on a digital sound synthesis chip developed by Yamaha in the mid 1980s. Among other things, it was used in computer sound cards, including the Ad Lib card and early Sound Blaster series. The OPL plugin emulates an OPL sound chip, providing all features of the OPL2 and some features of the OPL3. It also supports drag and drop importing of SBI files, an instrument file format developed by Creative Labs back in the day for the Sound Blaster. OPL even supports Percussion Mode, something that was barely documented, even for the original hardware.
discoDSP OPL is available now for $29. It requires an AU or VST plugin host.