Steam Support: All the data and settings related to your Steam account in one place.
Millennium: [steambrew.app] Themes and plugins for the Steam client.
CuSteam: [custeam.io] A homepage for the Steam Overlay browser.
DuckDuckGo [duckduckgo.com] A good alternative to CuSteam as startpage.
Humble Store: [www.humblebundle.com] My favorite alternative digital storefront for Steam games.
SteamCMD: A command-line version of the Steam client to run various dedicated servers.
OpenCritic: [opencritic.com] Review aggregation and game release calendar.
IsThereAnyDeal: [isthereanydeal.com] A price comparison and tracking service.
AugmentedSteam [augmentedsteam.com] A great browser extension for Steam.
SteamGifts: [steamgifts.com] Be the good you want to see I the world and give away your spare keys!
Steam Charts: [steamcharts.com] An ongoing analysis of Steam's player numbers.
Steam Services Status: [steamstat.us] Worldwide Steam services status information.
Steam Database: [steamdb.info] Insight into the applications and packages from the Steam database.
Idle Master Extended: [github.com] Get the Trading Cards for games you own but never play.