I'm developing this as an ideas system to make it very easy for users to suggest and vote on features they want to see in phpBB. It is based on the WordPress Idea Centre.
It has no dependencies (except for phpBB, obviousl), and is easy to theme. Sessions and users are bridged, as are styles (mostly).
It's currently still in Alpha, but if you want to test it then you can either register yourself (preferred; then you won't get "You have already voted on this issue" errors.) or bug me on IRC for the username and password to a test account. The one I linked to has ideas for phpbb-ideas.
EDIT: oh yeah, it's on github: https://github.com/callumacrae/phpbb-ideas/