Behold, a digital reproduction of the Moog Modular V synthesizer, designed to faithfully emulate the original instrument (including the instability of the analog capacitors and oscillators). The interface is absolutely nifty; to connect the various modules, you drag virtual patch cords between the inputs and outputs.
Even better: there are demo versions available for both Windows and Mac (OS 9 and X). You can't save presets, and there's a regular white noise which prevents you from recording (unless, say, you recorded a couple of different times and crossfaded between them to avoid the noise), but you can play around with it to your heart's content...
I don't know that I'd pay $329 for it, but it's still pretty neat.