projectM is an open-source project that reimplements the esteemed Winamp Milkdrop by Geiss in a more modern, cross-platform reusable library. Its purpose in life is to read an audio input and to produce mesmerizing visuals, detecting tempo, and rendering advanced equations into a limitless array of user-contributed visualizations.

github.com/projectM-visualizer/projectm

Foobar2000 component:

www.foobar2000.org/components/view/foo_vis_projectM