FluidSynth - FluidSynth is a real-time software synthesizer based on the SoundFont 2 specifications and has...
GarageBand - GarageBand is a fully equipped music creation studio for Mac
VirtualMIDISynth - VirtualMIDISynth is a software MIDI synthesizer implemented as a Windows multimedia user driver...
Ohm Studio - Ohm Studio is the first real-time collaborative digital audio workstation.
Zebralette - u-he makes creative software synthesizers and effects.
FL Studio - Image-Line's FL Studio, now on it's 12th version, is a well-known music production suite and the most popular beat processor on the market, due no doubt to its longevity. Read more about FL Studio.