YouTube Trending - Making it easier to find viral videos
Clicker for YouTube - The best standalone YouTube TV player for Mac
SimilarChannels - Find similar YouTube channels, discover new channels based on your interests, create your own YouTube collections with your favorite channels.
Youtube Detox - Distraction-free Youtube search
Vidooly - Get deeper analytics of any YouTube channel or video
YouTube Realtime - The true subscriber count for YouTube, with comparison too.