Last.fm has been around for a decade now, but the Internet radio and music recommendation service is still a reliable tool for discovering new artists.

Tie these characteristics to the same kind of artist-to-artist matching algorithm that fuels so many other music-discovery apps, and you have a uniquely intelligent system for finding new music. You can even base them on tempo, playing back a series of similarly paced songs. A playlist can be sensual, angry, happy, tender or some combination of all four. The options look broad, but are surprisingly powerful. There are at least a dozen apps that let you build a playlist based on related artists, but Moodagent factors in the mood of each song to build out something that feels more consistent. That’s because it takes standard algorithmic music recommendations and beefs them up with emotional intelligence. Since launching on Spotify last year, Moodagent has been one of the most interesting apps on the platform.

The thing for which they’re probably most useful is discovering music you might like but may never have heard otherwise. These apps perform a lot of different functions – some are social, while others sonically augment album reviews from big name publishers.

Spotify’s app directory now features almost 60 HTML5-based add-ons for the service’s desktop client.

Spotify music discovery