Many years ago I was amazed of SumSynth idea by Lazyfish. It was outstanding because Lazyfish found a way to construct fully operational spectral synthesizer whereas Reaktor had no actual multi-sine modules. Nowadays Reaktor has Sinebank module and it's a quite revolution for the software. Having hundreds and hundred of sine waves mixed together you can get almost any sound possible! And now Razor synth introduced by NI and Errorsmith is really new breathe take in additive synthesis!