Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
SoundGrail - SoundGrail Music App designed for pianists, guitarists, and DJs.
LMMS - Make music with a free, cross-platform tool
keezy - A colorful soundboard. Play with music.
Oceanaudio - Ocenaudio is a cross-platform, easy to use, fast and functional audio editor.
Splice - Music creation, collaboration, and sharing made simple.