vdNote is a really cool way to watch and share noteworthy moments in YouTube videos. Paste a link of a video and start watching. Start typing a note at any moment and the video stops while you write. It then timestamps your note to that point in the video so others can see the context. It's even easy to share a note to @twitter!
Dnote Browser Extension is a tool to capture your everyday learnings instantly without a distraction. It sends you a weekly digest email to help you actually remember what you learn.
It supports Chrome and Firefox.