TabFloater - Browser extension to use picture-in-picture with any website
CONV. - Convert YouTube video to MP3, GIF or MP4
Video Hub App - The fastest way to browse, search, and manage videos on your computer. Like YouTube for videos on your computer!
Downie - Video download for OS X. Downie supports at this moment over 1,000 different sites.
riv.yt - A minimalist way to view and share YouTube videos
Yout - YouTube to Mp3 Converter