Also wiki would look ugly except you put each of your items into a custom <foo></foo> element, which makes stuff just more complicated, and then the width limited layout of the current css makes it even more unusable for it. So in the end no one would use it ...
Making a document in gobby/etherpad is limited per se by the using of a textformat.
At first I hoped that github would feature such project management capabilities, but it seems it doesn't.
But web2.0 let grew a lot of such projects, so here my 2 results of a short internet search:
http://www.teamworkpm.net/features-tasklists
http://whodo.es/explore/task
None of those satisfies me. There are many other sites in the web2.0 cloud but collaborative functionalities seem rare and when they exist they cost money, so finding the right one seems pretty hard
