Magic Playlist - Get the playlist of your dreams based on a song
Steam Charts - An ongoing analysis of Steam's concurrent players.
Spotalike - Spotify playlist with similar songs, according to Last.fm
Steam Database - This tool was made to give better insight into the applications that Steam has in its absolutely huge database.
Playlist Machinery - Tools that help you create & organize your Spotify playlists
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.