OB-Xd is based on the Oberheim OB-X. It attempts to recreate its sound and behavior, but as the original was very limited in some important ways a number of things were added or altered to the original design. OB-Xd was designed to sound as good and as rich as the original. It implements micro random detuning which is a big part of that sound. It's available as AudioUnits, VST, VST3 and Standalone app.
While not copying originals, some of the features were taken to a better point. Continuous blendable multimode filter (HP-Notch(BP)-HP in 12 dB mode and 4-1 pole in 24 dB mode). Also, like many synths of the OB-X's generation, the OB-Xd has no internal effects so its sounds and textures can be greatly enhanced by the use of additional processing like chorus, reverb, delay, etc.
Thanks to 2Dat for the original OB-Xd and Soshi Studio for giving the rights to continue this wonderful product. Also thanks to all KVR artists for making the amazing skins!. OB-Xd Desktop has no restrictions and is free to use. Buy to support further development, thank you! Source code is available under GPL license at GitHub.