google groups(mailing list),
google drive/docs (iirc),
heck there is probably a twitter facebook and g+ too
The problem is many people think of their favorite tool/tech and then shoehorn it in. It should be the otherway around -- what forms of communication does the project need and THEN what tools (in use by the project or new) can be used to meet that need.
I'm also taking a view of "getting things done." We are not enterprise. We are not corporate. We are not trying to invent some new open source workflow method. We are to make a game and, so far, all of this.. stuff is getting in the way. We are long past the point of arm chair debates and already considered by most dead on arrival, if any arrival is to be had. I made multiple posts on this weeks ago. I know progress has been made but a lot of wheels are still spinning in "look at all this work on web tool stuff we are using!" Also how many bloody accounts on how many websites are needed for developers and very interested parties to keep up?
First need is the social media/public outreach/pr type of things. Honestly it isn't needed and kind of pretentious at this point. Wait until there is something playable and, in its own way, fun, before doing public outreach and social media. The developers who are (still) interested are already here. If we can't make it to that point (milestone 5ish?) then the project is dead anyways.
There is bug/todo/etc list that has now been added to the forum. That can be handled by the forum OR via the github issue and milestone system. There is a very good reason github calls it issue tracker and not just a bug tracker. It is also designed for the git workflow (pull requests).
Discussing ideas: Right now this is divided over the forums, trello, reddit, maybe the google group (which, honestly, I am not subscribed to). There is conversational discussion, postulating, and development, which irc does well. But engine design and game development is very nuanced and requires paragraphs to fully articulate and support ideas. Forums are great at that. Trello was started because the forums were "too chaotic," in reference to posts drifting into related but technically off topic subjects and cross referencing other posts. The Trello is now showing signs of the same issues. Forums do the same thing that trello does: categories, votes, comments. It is an issue of moderation, not tooling. The other issues is that while individual design ideas should be evaluated/prototyped/discussed on their own merits they also have to be discussed in the context of other designs and philosophies and requires cross referencing. If moderation or the forum tools isn't up to the task then we should look at improving the forum tools such as moving to Discourse or perhaps some other developer centric discussion software.
There is perhaps also a need to put more finalized documents. A wiki is suppose to be an open (or almost open) database. It is as one poster put it "git for words." So far when most people say "wiki" they really mean "content management system" that is edited by only a curated few. There is nothing wrong with a cms, but don't confuse the tool (mediawiki) with the function (is it a wiki or a cms). I don't see a wiki working well with game dev workflow. A forum topic can work well as long as the op (a dev) is active and keeping the top post up to date. phpBB also has several addons for cms type functionality in making pages. Github issues also work here too. Again, issue of moderation and not tooling.
So that is where I am at with our needs. Real time conversation, longer essay type discussions, programmer/art workflow, and maybe a place for formal final documents. Irc, forums, github, cms (or even still the forums).