CONV. - Convert YouTube video to MP3, GIF or MP4
Wibbitz - Watch video summaries of the news you want.
Softorino YouTube Converter - Download YouTube video & audio. Watch and listen offline
GIFit! - Quickly turn YouTube videos into GIFs (chrome extension)
You-Get - Command-line utility to download media contents from the web
Youtube Plus - Home of the extension YouTube Plus that allows you to experience more on YouTube - ParticleCore/Particle