ActiveMail is a Safari, Firefox and Google Chrome add-on that makes your emails interactive and feature-rich.
When you receive a video from YouTube, you will be able to watch and comment on it directly from your inbox.
Also, you will be able to comment of Facebook or tweet a message without leaving your email client.
ActiveMail supports Gmail, Hotmail, Yahoo! Mail, Outlook and a dozen of the Web’s top video sites, plus online albums and slides.
ActiveMail is cross-platform and it works on Mac OS X, Windows and Linux.