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.
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.
Latest binaries can be downloaded at https://www.discodsp.com/obxd/
Source code can be compiled with JUCE 7.0.3.