Dexed

This is the best Yamaha DX7 emulation in the freeware world.
The plugin is closely modeled on the architecture and sound characteristics of the legendary DX7. In fact, it is even capable of loading the original SysEx programs for the DX7, hundreds upon hundreds of which are freely available on the world wide web.
http://bedroomproducersblog.com/2014/06/15/digital-suburban-dexed/
https://github.com/asb2m10/dexed