These folders will probably be changed soon to a more SVN-friendly scheme.

Here's the description for the main SVN folders:

/as2_fl7 : Tweener source classes, Actionscript 2 version, without advanced features such as filters. Must be used on AS2 projects (when targeting Flash Player 7+, and Flash Lite Player 2+). /as2 : Tweener source classes, Actionscript 2 version. Must be used on AS2 projects (when targeting Flash Player 8+). /as3 : Tweener source classes, Actionscript 3 version. Must be used on AS3 projects (when targeting Flash Player 9+, including when using Flex). /as3_swc : Same as /as3, but in SWC form.

/branches : Other code branches, for experiment and test purposes. They're not guaranteed to work, so nobody should usually download them.

/docs : Documentation, in various shapes and forms (HTML, Flash IDE, Help Toc, etc). /examples : Example files with source.

For more information on which version to download, please visit: http://code.google.com/p/tweener/wiki/WhichVersionToDownload