Facebook Gaming - Watch and stream live games on Facebook
Steam Inventory Helper - Steam Inventory Helper is a free browser extension for Google Chrome that adds a big amount of new features into the Steam trade-offer system & Steam store functionality.
Mevo by Livestream - The live event camera
Augmented Steam - Enhanced Steam fork by IsThereAnyDeal.
Twitch Creative - Watch artists create. Twitch expands into the arts.
Steam Tools Hub - A set of Steam related WebApps built around trading cards, emoticons and backgrounds.