I have released "Knowledgetree Zimlet" on the launchpad a few days ago.
Basically, the zimlet enables drag and drop approach to zimbra users so that they can save email and all its attachments in a single .eml format to knowledge tree. Additionally, user can click on a link added after download link of each attachment to save only the document they want.
I'm currently looking for participants or testers to help me find bugs and do feature requests for the next release. As now I'm working on my own and think it might be better to receive some new ideas from others.
If you have any problems or questions please feel free to ask.