Mosoto is a Web-based app for Facebook, giving you a virtual desktop with chat, music, and file sharing built right in. Mosoto allows you to chat with other Facebook friends and swap photos, music, and videos using a shared storage folder from Box.net. As a service, Mosoto is meant to replace desktop applications for chatting and music.
The music player's user interface takes a design cue from iTunes. Double-clicking a song starts playing it instantly, almost like it's running off your hard drive--a good use of streaming. You also can quickly make playlists with simple drag-and-drop functions. There's no album art for music tracks, which is a little disappointing. Adding your own files is intuitive and handled through the centralized uploader. Again, this is linked to your storage from Box.net.
Unlike the glorified message board that is Facebook, Mosoto enables you and your friends to interact live. The interface is reminiscent of Meebo, with hierarchical buddy folders, and features that let you set your online status and check buddy information. The chat windows themselves give you Facebook-centric options like poking, viewing user profile, sending a message through Facebook's e-mail, and adding people as a Facebook friend. You also have the option to check out users' shared media folder to view their content.
As a Facebook user I can see the use of Mosoto, but I wouldn't necessarily pick it as a replacement for iTunes and Trillian (the two apps I use for chat and music). I see elements of Mosoto fitting in as widgets, or something to be added to Facebook as a feature. Mosoto still ties into your Facebook universe, but in a way it feels somewhat distant and removed. Despite this, Mosoto is still slick and a smart application of Facebook's API, not to mention it's the first real IM for Facebook users. It will be interesting to see whether people will use it instead of their chat and music apps.
Mosoto is currently in private alpha, with the intent on a public launch next month. In the meantime, you can sign-up for Mosoto testing here.