Windows: If you've been using Steam for a few years, chances are you have an unwieldy list of games in your library's sidebar. While you can categorise them into folders within Steam manually, Depressurizer helps automate the process.
For the app to work, you'll need the Microsoft .NET Framework 4.0 and a public Steam profile. When you run the application, it will find your Steam library and list all of its games. Just hit Tools > Auto-Cat to automatically assign games to different genre folders such as Action, Adventure or Casual. It might not work for all of your games, but it should take care of the lion's share, leaving you to only drag and drop a handful manually. Once you're done, hit Profile > Export Config File, restart Steam, and your library should be cleaned up and categorised. The app is a little buggy, and you might see quirks such as UI buttons slightly cut off at the bottom of the window, but you only really need to use it once to get your library in order.