projectM is described as 'LGPL'ed reimplementation of Milkdrop under OpenGL. All projectM requires video card with 3D acceleration and your favorite music' and is an app in the Photos & Graphics category. There are more than 25 alternatives to projectM for a variety of platforms, including Windows, Android, Android Tablet, Winamp and Steam. The best alternative is MilkDrop, which is both free and Open Source. Other great apps like projectM are Magic Music Visuals (Paid), Avee Player (Freemium), VSXu Ultra Artiste (Free, Open Source) and Kauna (Free).
Powelus's Audio Visualizer allows any person to customize visualizer to their own experience. The software has the capability to load local MP3 files and display audio spectrum during real-time playback.
NestDrop allows you to perform with high-resolution high-fps visuals which react in realtime to the music and then broadcasts the video via Spout. Since the Milkdrop engine is at the core you can easily bring in your own Milkdrop presets.