The Return of Rebirth    

ReBirth emulates two Roland TB-303 synthesizers and a Roland TR-808 since v1.0,[5] and also a Roland TR-909 drum machine since v2.0. All emulations can be used simultaneously. Each of the emulated devices has its own pattern selector, a feature the original devices are lacking. This allows fast switches between different musical sequences, and re-programming the TB-303 for playing different notes, for instance, is rendered unnecessary. This feature has been adopted in some of Reason‘s devices. ReBirth also features mixers, a pattern controlled filter (PCF) and some of the standard effects in software synthesizers like delay, compressor and distortion.
The program also supports user modifications, which may replace the samples in the drum machine emulations and modify the GUI. There are four modifications included in the ReBirth installation by default (though the default ReBirth GUI seems to count as a modification as well).

The virtual knobs and controls can be assigned to physical counterparts via MIDI, so knobs, modulation wheels, faders and other performance controls available on keyboards and modules can be used to shape the software sound.