Joost is not a new energy drink, apparently.

Joost.com is "a new way of watching TV on the internet". Currently in (much coveted) beta testing, Joost will provide users with high-quality full-screen picture, hundreds of full-length television shows and YouTube-esque viral videos. Joost will also incorporate instant messaging and social networking features. It is completely free, and works with most modern PCs and Intel Mac-based computers with a broadband connection.
The down side? I don't have it yet.