TubeLister - Generate a YouTube playlist from your opened tabs.
Yout - YouTube to Mp3 Converter
OrganizeTube - Create video playlists from Youtube, Vimeo and other sources
Softorino YouTube Converter - Download YouTube video & audio. Watch and listen offline
Learnamic - Free and paid K-12 learning resources from hundreds of providers, including educational apps, YouTube videos, online classes, printable worksheets, and more.
CONV. - Convert YouTube video to MP3, GIF or MP4