Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Soundplant - Play sound files with the computer keyboard
Magix SpectraLayers - SpectraLayers Pro transforms sound into a unique visual world of multidimensional audio data.
CasterSoundboard - A soundboard for hot-keying and playing back sounds. (For podcasting)
Acoustica - Acoustica is an audio editing tool for editing, mastering and restoration work on both Mac and PC.
JN Soundboard - An open-source hotkey soundboard program