Aparillo is a strange and wonderful beast. It's an interesting take on a well established form of synthesis - FM. Like the classic DX-7, it uses sine waves to modulate one-another to create complex, rich timbres. But where the DX-7 had 8 operators, each with it's own multi-stage envelope, Aparillo uses just 4 operators that share a single ADSR envelope. It's relatively easy to wrap your head around so if you have a bit of an understanding of FM synthesis, you won't have any trouble making a few basic patches with that distinctive FM edge to them. But that's just the start of what Aparillo has to offer because it has 16 copies of this set-up ready for you to modulate and sequence in amazing ways.
The UI gives away the main game - the prominence of the LFOs in the centre of the interface tells you straight away that they are central to what Aparillo can do. Crucially, the interaction of the LFOs adds unique qualities to the results you get from this instrument. The LFOs are used to offset the 16 voices to provide anything from a subtly shifting thickness to the sound or complete mayhem. Add in a simple sequencer that plays off what's happening with the LFOs, sequencing each of the 16 voices in turn, and you've got yourself an absolute monster of a synth. But that's still not the end of it.
Lastly we have the Orbit, which is a dynamic, visual tool for provoking even more modulation/mutation of the sound. It consists of 16 widgets for each of the modulatable parameters, including some effects parameters, plus the Orbiter, which is the control element. As you move the Orbiter around it connects with different parameter widgets and as it gets closer to a widget, the amount of modulation on that parameter increases. You can record the movement of the Orbiter to create a patch that morphs over time in a very natural, organic way or you can set it up statically to add an extra layer of modulation to any parameter(s).
As I mentioned, there are also effects - a filter, a delay, a reverb, a panner and a spatialiser effect that can do some pretty cool things. The effects sound great but they lack a lot of control. e.g. You can't control the delay feedback, which is set quite high, so it's not always useful. They have their uses, though, and as their controls can be modulated, they add a bit extra to the sound design process.
Aparillo is a great synth but it is not without it's limitations. There are a few missing modulation sources. It would be nice to see aftertouch included in a future update, as well as maybe a few key MIDI CCs to add more hands-on control. As it stands, though, there is still plenty of scope for making lots of unique, amazing sounds. It's probably not going to be anybody's go-to synth but when you're after something weird and whacky, it could be just the thing. BTW, the blurb reads like it might be a monosynth but it's not, you can play chords and get all 16 voices per note.
EDIT: I changed the rating to 5 stars when I realised that the Orbit section allows you to add a second modulation source to any or all parameters. I also changed the text to highlight this.