The simplest use case for TweepML is to allow sites or individuals to create a downloadable file that contains a list of Twitter users, allowing others to import the file and follow all those users easily in one fell swoop. Imagine for example the popular Follow Friday tradition on Twitter -- instead of trying to cram a big list of tweeps into 140 characters, you could simply create a TweepML file and point your followers to that.
Like OPML, TweepML is based on XML, a textual data format and open standard in wide usage on the web. Companies and individuals will be able to take the simple and extensible architecture of TweepML and build extra functionality and applications on top of it, all without having to pay hefty licensing fees or get anyone's permission to do so.
TweepML.org Service
The TweepML format has been officially approved by Twitter and launches today, with a companion service at TweepML.org that provides a basic TweepML editor for creating your own files with groups of Twitterers, and a Follow tool that takes a TweepML file as input and allows you to easily select which users from the list you'd like to add as followers.
You can either create and save TweepML files and save them on the TweepML.org site itself in order to get access to list management tools and statistics about your list usage, or simply save the TweepML files you create to your own desktop for use on your own server or site. You can see some of the lists already created so far, and if you're curious about the syntax, you can check out some examples here.
If you like, you can also add the entire Mashable team in one go via our TweepML list.