I just finished building a Trac instance for Foolscap, now online at http://foolscap.lothar.com/trac . It's got a (mercurial-based) code browser, tickets, and a wiki.
Setting it up required some twisted.web hacking, because my setup puts a twisted.web server out front, and reverse-proxies certain requests to a separate Xen virtual machine which handles all CGI (for multiple sites, like buildbot.net and foolscap.lothar.com). That CGI host is running apache, and since URLs inside returned pages are not being rewritten, I had to use named virtual hosts to distinguish between, say, http://buildbot.net/trac and http://foolscap.lothar.com/trac .
But the normal twistd.web.proxy ReverseProxyResource clobbers the Host: header when it forwards the request (setting it equal to the new host being targeted). I suppose this is to hide the presence of the proxy from the new host, but in my situation is has the effect of making it impossible to use vhosts on the apache side to distinguish between requests that were received for different hostnames.
So I subclassed and commented out that line, and apache is happy. Now that I can have more than one trac instance on this box, I'm creating Tracs for everything. Whee!