Google Summer of Code/2013/Ideas/Tags support for Portage
Gentoo uses categories now. A package can only be in a single category, which is very limiting because generally things don't fit perfectly into one place without other possibilities. Tags could make it a lot easier to find packages they're looking for by doing Boolean searches like: kde AND mail. This project would add support for tags to Portage and would allow for backwards compatibility of categories as tags.
This project in its current form is considered trivial and not suitable for a complete SoC project . If you wish to work on this, you should expand the scope of the work significantly. One possibility is to include the Portage public API project already partially completed.