What I'd love is a replacement for PHPbb that wasn't only accesible via web.

Basically make it possible to write readers without the overhead and trouble of HTML and CSS. There's really nothing in the basic principle of a forum that requires the web... it's just text in a predictable format, like e-mail. Actually simpler than e-mail. It'd be great to have a native 'forum reader' in the style of a newsreader for System 7. Actually that's pretty near the top of my app wish list for any platform...