The PPG Realizer was the first digital virtual synth. Pictured below you will see a number of knobs with lines for each making it's way to the green monochrome monitor. In that monitor you might recognize something very familiar - the Moog Minimoog. That's right. The PPG Realizer was to have a model of the Minimoog back in 1986! It was to be the ultimate synth in its ability to host software versions of other synthesizers. Unfortunately it never made it to production and it put PPG out of business. Click through title link for more and make sure to check out the rest of the site. It is a fantastic PPG resource.
Amazingly ahead of it's time:
""An impressive exhibit from PPG was the Realizer (about $50,000). This consists of software versions of familiar synthesizer configurations. It allows you to design your own analog, FM digital, and sampled sounds, patch any of the components of one instrument into another instrument, and then sequence or sample the resulting sound. Wolfgang Palm, designer of the Realizer and head of PPG Instruments, earns the quote-of-the-show award for explaining how he designed it: 'I copied the circuit diagrams into software.' No easy task."