Enhanced Steam is an unofficial browser extension and website designed to improve the Steam platform experience for users. It adds a number of features to the Steam website, including enhanced price comparisons, game suggestions based on your library, custom filters for the Steam store, and the ability to track your Steam achievements. It also provides an in-depth view of game histories, reviews, and pricing information, and can alert you when titles on your wishlist go on sale. Enhanced Steam also allows users to create custom collections of games, and to keep track of their Steam friends and achievements.
Steam Inventory Helper
FreeSteamKeys
Steam Trader Helper
Steam Tiles
Warning The extension is requesting dangerous permissions and is reportedly monitoring and sending your online activity to its own server, for promotional stuff it seems: https://www.reddit.com/r/GlobalOffensive/comments/70xofs/warning_trusted_steam_inventory_helper_now/