You can easily add chat and other real-time collaboration features to your website with the TogetherJS library.
The Print YouTube bookmarklet creates a contact sheet from any video. It extracts the storyboard frames of a video, stitches them all and sends it to your printer.
LinkedIn, the social network for professionals, sends too many email notifications and they also make it difficult for you to unsubscribe from these emails. There's an easy workaround though.