Bookmark OS - Bookmark OS is like Mac or Windows optimized for bookmarks.
Bookmark It - Create awesome notes on YouTube videos
Raindrop.io - All your articles, photos, video & content from web & apps in one place.
PageMarker - Save, organize, annotate and revisit your bookmarks
Twitter Bookmarks - Create shortcuts to your favorite users/tweets on Twitter
Stationian - Stationian bookmark manager intelligently analyzes the websites you saved and determines the best way to present them without needing to go to the website.