Synthmaster from KV331 Audio is a multi-mode, multi-engine beast of a software synth with power for serious sound design. Its capabilities run the gamut from additive to virtual analog (subtractive) to wavetable to sample playback. For those who don't wish to get deep into programming, its presets are equally varied and versatile.
They're so versatile, in fact, that a lot of musicians want just the presets and a handful of most-often-grabbed editing controls. Not unlike instruments in Logic Pro, these controls change to be most appropriate to the preset you have called up.
There are actually two versions: The "regular" Synthmaster Player costs US$29.99 and comes with 1,700 presets. The free version, which the webpage understandably calls less attention to, comes with 500 presets. But it is there, with download links at the very top right, in fact.
Back when I was editing Keyboard magazine, we reviewed an earlier version of Synthmaster in the April 2014 issue, and Jim Aikin called it "a real sleeper of flexibility and power" and "so good it's scary." My own experience bears this out, and if you need lightly editable presets covering everything from a straight-up Rhodes to Vangelis-like pads to screaming leads to highly animated, burbling motion synths, the Player version covers it. The free Player is definitely meant to be the gateway drug to the rest, but keep in mind as well the full version with the deep editing interface costs only US$99.
Whichever one you pick, it really is one of the best "sleeper" values out there. It also plays nice on Mac or Windows, with 64-bit versions available for both. Get it here.