projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
Mixed in Key - Mixed In Key is award-winning DJ software that gives you the #1 technique of the world's best...
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
beaTunes - Smart software for library management, music analysis, and playlist creation. For Windows and macOS.
Free Audio Editor - Free Audio Editor is a sound editor program for Windows.
Tunebat - A browser based song key and bpm database. Supplies compatible songs for harmonic mixing.