Annotate.tv - Optimize your learning on YouTube
Raindrop.io - All your articles, photos, video & content from web & apps in one place.
Mochi - Write notes and flashcards with Markdown and study them with spaced repetition.
Pocket - When you find something you want to view later, put it in Pocket.
Jot - The no-fuss way to take notes
Basket - A note taking application for KDE. Lots of features.