Paul Lamere in Building a Spotify App:

Developing a Spotify App is just like developing a modern HTML5 app. You have a rich toolkit: CSS, HTML and Javascript. You can use jQuery, you can use the many Javascript  libraries. Your app can connect to 3rd party web services like The Echo Nest. The Spotify Apps supports just about everything your Chrome browser supports with some exceptions: no web audio, no video, no geolocation and no Flash (thank god).

In case you missed it, we launched a Preview version of Spotify last week with support for apps. If you’re interested in building your own app, be sure to read Paul’s article.