Steam has added yet another sweet new feature to its beta client: Tags. While it sounds rudimentary, the new system allows users to add their own tags to games, which then fuels new sorting and even personalised recommendations.
While Steam is a great gaming client, the store hasn't always been the best for casually browsing (except during Steam sales). By allowing users to tag games, the company is building a database of metadata that will be used to power recommendations.
In the initial release, somewhat unfortunately, you can't use your own tags to sort your personal library, but you can add as many as you want to help fuel the system. If you want to get started, you'll need to download the beta Steam client.