d-lusion's Rubberduck Music software company d-lusion recently made availabe their Rubberduck program for free. It’s based on the Roland TB-303 and according to their website it was released before Propellerheads’ Rebirth software. Link (via slashdot)

With this bass synthesizer released for Windows 95 in 1996 (way before Propellerheads Rebirth, was available), d-lusion pioneered the market of realtime software synthesizers on standard processors. Roughly based on the the well known TB-303, Rubberduck’s synthesis model consists of an oscillator wave with a resonant filter sweep applied to it combined with an efficient hardware sequencer design which resolves in the typical twisted, screaming, bubbling bass sound that is often used in Acid House, Goa Trance, or Techno productions. Rubberduck featured realtime digital resonant dynamic filters, frequency and volume envelope (DCA, DCF), 4 basic waveforms, dual oscillator sound generation (starting with version 2.0), a 224 note sequencer, a drum section where samples could be synchroneous played back, an effect unit delay/feedback/distortion) and was fully Windows 95 compatible. User feedback was overwhelming, ranging from “the door-bending bass response makes rebirths 303 section sound like a touch tone device” to “fucking brilliant” and the most famous quote which says it all: “it is like fucking a hot hollywood bitch for the price of a corner crack slut”. On the other side Rubberduck received impressive press couverage, from “KEYS” to “Future Music”.