reEmbed - Custom YouTube Video Player
CONV. - Convert YouTube video to MP3, GIF or MP4
TabFloater - Browser extension to use picture-in-picture with any website
Downie - Video download for OS X. Downie supports at this moment over 1,000 different sites.
Vid Repeat - Loop YouTube videos for X minutes or for X times. Loop a full video, or only a selected part, add a delay between the loops, and share the loop with your friends.
Yout - YouTube to Mp3 Converter