tunesBag is a free online audio library where you can store your music, create playlists and share with friends and other users.

Unlike other services tunesBag currently puts no definite limit on how much you can upload. However, they expect fair use, and should you intend to upload more than 5 to 7 GB, you will want to get in touch with them. Supported files are mp3, m4a, wma, and ogg.

There are multiple ways how files can be added to the library. There’s a browser and a desktop uploader. Files can be mailed to the library or uploaded from a source on the web.

Using the desktop uploader, whole iTunes and Winamp libraries or specific playlists can be uploaded automatically.

With the desktop and browser uploader, tunes can be added to your tunesBag playlists right away. The cool thing is that when you cancel an ongoing download, it will complete uploading the current file and pause until you decide to resume the upload process. So when you need some bandwidth, don’t hesitate to “cancel”, you can resume anytime.

In the library you can sort your music by genre, artist or album. There are various options for each song, such as adding it to a playlist, sharing, commenting, lyrics, videos, and through this menu you can edit and download the song.

Next to each track is a rating option from 1 to 6 points. In the sidebar to the left you’ll see that there are some basic playlists based on friends’ stream, recently added, recently played, recommendations or top rated items. Furthermore, your custom playlists, bookmarked playlists from other users and your search history are listed in the sidebar.

Integrated social services include Facebook, Twitter, Friendfeed, and Last.fm. Furthermore, whenever you listen to a tune, a sidebar opens to the right that features recommendations and comments, based on what you’re currently listening to.

Using tunesBag you’ll see more useful features. For example when you search for music, results you’re interested in will open in tabs. In the meantime you can continue listening to your library or playlists, which run in their own tab while you’re busy finding new material.

At the very bottom of the page you can manipulate the playback, add a track to one of your playlists, rate or share it.

Taken together, tunesBag is a very convenient service, which allows you to store your favorite music online, making it available to yourself and your friends wherever you go.

Should you ever lose the local copies of your collection, you can restore your music, i.e. collectively download playlists or your whole media library, using the desktop uploader.

tunesBag has been in private beta for quite some time. However, it appears that invitations are sent out frequently. I received mine only a few days after signing up. Additionally, I have 15 invitations for MUO users (update: we got another 100 invitations, see below). Leave a comment or request your invitation directly through Tina at MakeUseOf.com and you shall be rewarded. First come, first serve.

UPDATE: Signup up with TunesBag here (100 invites)