Steam Charts - An ongoing analysis of Steam's concurrent players.
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.
Steam Database - This tool was made to give better insight into the applications that Steam has in its absolutely huge database.
Steam Tools Hub - A set of Steam related WebApps built around trading cards, emoticons and backgrounds.
Augmented Steam - Enhanced Steam fork by IsThereAnyDeal.
Steam Market History Plus - Steam Market History Plus is a browser extension that comparatively provides more valuable Steam market history.