Annotate.tv - Optimize your learning on YouTube
Magic Music Visuals - Fully-customizable and highly responsive visuals for live and recorded audio & MIDI.
Slid - Capture knowledge from online videos, courses, and webinars
projectM - projectM is an LGPL'ed reimplementation of Milkdrop under OpenGL.
SkillTube - A curated list of best courses from YouTube & other platform
Kauna - Kauna is a music visualizer. Kauna renders any sound reproduction in system.