Other apps include TuneWiki which lets users read the lyrics in sync with the songs that they are listening to. Apps like Songkick let users find out if any of the artists in their library are performing nearby and provide an easy way to purchase tickets. To add apps, just head over to the left sidebar of Spotify and click on the section called App Finder, and select what you want/need.
At the moment there are only a handful of Spotify Apps, but you can be sure there will be a lot more available in the future.