Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Matchering - Open-source audio mastering app that masters music based on any reference track you provide.
Reaper - Reaper is a focused digital audio workstation (DAW) developed by Cockos. In the creation of the software, the digital audio technology company intended to make audio editing accessible to the masses.
Lurssen Mastering Console - Digital audio mastering powered by years of pro-quality mastering experience.
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.
Audio Mastering - Pro quality, fully functional audio mastering application for iPad.