Previous to and now in parallel with I've been using DokuWiki? for various documentation purposes. Other than multi-project support the main thing I'd like to see in Trac is some way to do simple diagrams online. DokuWiki? has a really neat (although aging) plugin that integrates the JHotDraw applet into the wiki (www.jhotdraw.org); the way this works is it creates a diagram and saves it to two formats - and editable text format (internal to jhotdraw) and an image file which is displayed in the wiki (until the edit button is clicked, which loads JHotdraw with the text descriptor to allow edits). This allows simple things like squares, circles, and lines to be quickly created inline in the wiki, its not any sort of UML editor, but for quick explainations it avoids the need to pull up an external program, sort the files somewhere, and then upload and image to Trac. I see someone else requests Gliffy support, which would accomplish something similar, except the jhotdraw is an open source project.