We had previously developed a range of Subtractive synthesizers (like 3xOsc, SimSynth, Wasp, Sytrus (50%) & Poizone) and 3 FM Synths (Sytrus, Toxic & DX-10) but we didn't really have an additive synth (other than Beepmap, which is more for special effects sounds).
Now that CPUs are gaining the power required to handle additive synthesis we decided to do a decent additive synth also.
The FL Studio Support Team