Spectro - Spectro is a freeware audio file analyzer for windows.
Serum - VST for FL Studio, Ableton Live, and many other VST supported DAWs. Heavily utilized in EDM.
Lossless Audio Checker - A utility to check whether an audio file is truly lossless or not.
Surge XT - Open-source subtractive-hybrid synthesizer formerly sold commercially as Vember Audio Surge.
Friture - Friture is a program designed to analyze audio input in real-time.
Omnisphere - Piano, pad and synth VST for DAW's.