Bookmark OS - Bookmark OS is like Mac or Windows optimized for bookmarks.
Vidooly - Get deeper analytics of any YouTube channel or video
BookmarkSheet - Your bookmarks in Google Sheets
SimilarChannels - Find similar YouTube channels, discover new channels based on your interests, create your own YouTube collections with your favorite channels.
Annotate.tv - Optimize your learning on YouTube
YouTube Trending - Making it easier to find viral videos