Yout - YouTube to Mp3 Converter
Vidooly - Get deeper analytics of any YouTube channel or video
Softorino YouTube Converter - Download YouTube video & audio. Watch and listen offline
SimilarChannels - Find similar YouTube channels, discover new channels based on your interests, create your own YouTube collections with your favorite channels.
You-Get - Command-line utility to download media contents from the web
YouTube Trending - Making it easier to find viral videos