As the name suggests, everything going on in here is pure synthesis. Specifically Frequency Modulation (FM) synthesis, in a striped-down form. You still have some modulation options, but not as much as you would have in a more traditional FM Synth like DXi. EPS is offering only two modulators and two LFOs for added Tremelo and Vibrato. A delay effect, as well as a Tube Overdrive, help to thicken out the sound.
The limited controls allow it to cram everything on to one screen. This is nice when you're playing, but at the heavy cost of articulation in envelopes. Modulators are limited to just a Decay envelope, and the voiced carrier only offers Decay/Release. All of this adds up to a very simplified version of FM that should be more approachable for new users. Other features greatly extend the usefulness of this app; including Virtual/Core MIDI, Recording and Audio Pasteboard.
Disclosure: I received my copy for review from Bacaj Apps.