Steam Charts - An ongoing analysis of Steam's concurrent players.
The Internet Arcade - 900+ classic arcade games, no quarters required.
Steam Database - This tool was made to give better insight into the applications that Steam has in its absolutely huge database.
Revi Box - Receive a box every 3 months to support refugee schools
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.
GameTree - Discover the friends and games you will love most.