Rutt-Etra-Izer, GLOW, Chrysaora
Rutt-Etra-Izer

Rutt-Etra-Izer (WebGL app) by Felix Turner is an implementation of a video synthesizer. Simply drag and drop an image file to the browser, and it’ll render a 3D version using lines.

Different images have varying effects, so it’s fun to experiment. Rutt-Etra-Izer is built with three.js.
GLOW
GLOW (GitHub: empaempa / GLOW, License: MIT) by Mikael Emtinger is a WebGL API that focuses on shaders. The authors also worked on the impressive ROME – Three Dreams of Black project.
There are tutorials on the GLOW site, including one which shows how it can work alongside three.js: Hello Three.js.
Chrysaora

Chrysaora is a WebGL demo by Aleksandar Rodic. There’s a lot of background material about the project on Aleksandar’s blog.