This is my workhorse synth. There's a very large 'sweet zone' for patch creation, and this is what I like the most.
The oscillator section is fantastically flexible. Contrary to most synths, where you only have a mixer to combine the oscillators, here you have morph and meld. What they do is to attach two waves, similar to what phase distortion in Casio's CZ series did. When the morph slider is in the middle, the resulting waveform contains half a cycle of both oscillators. Moving the slider cuts off the cycle of one waveform replacing it with the cycle of the other.
The oscillators have the typical saw, square (pulse), ramp, triangle, sine, pink and white noise. But they all respond to PWM (!). If that wasn't enough, you can draw the waveform. Forget about other implementations: this is the best waveform drawing interface I know.
Osc C can FM A, B or both. The LFOs run at audio rate, so you could use them as FM modulators. That is, you may not recreate all algos from a DX7, but you could get pretty close. 3 LFOs, 3 oscs. No self modulation though.
The envs are very snappy and flexible. You can invert them, have delay, initial volume level... and each stage can be modulated (!). I've not seen this before. Huge flexibility.
The filter is sweet, and has less obvious modes such as, DLP - Distorted Low- pass, PLP - Parallel detuned Low pass, FORM - Formant filter and MOOG - Moog LP filter.
The range of sounds Kruudster can produce put other free, and paid, VSTs to shame. I have no idea why this plugin is not more popular. The dev deserves all respect in the world.
The manual is only 3 pages, but the >300 presets show what this monster can do. Growl basses, chiptunes, huge pads... it's all there. It doesn't need unison to sound fat. The modulation options are outstanding, and pretty easy to visualize (it's a one-page synth). I have other paid synths, but spend most of my time on Kruudster.