Some degree of infrastructure is needed to collaborate, communicate and distribute online for open source game projects.
There are many free software project hosting facilities that provide services useful to open source game project.
Use Git or Mercurial. Do not use CVS or Subversion.
Communication between the game creation team, contributors and players can happen on many different channels.
An online website for project news allows to keep readers, reporters and contributors up-to-date about releases and development. Use it as a PR platform.
Atom/RSS newsfeeds allow users of feed readers to efficiently follow your blog and make it possible for you to easily pipe news into social networks.
When there is no demand for a forum yet, it is recommended to start a thread on a related feedback forum like for example on the FreeGameDev Projects subforum.
Mailing lists can be efficient for development discussion but are not as accessible as web forums.
As IRC has a relatively steep learning curve for new users, it is recommended to provide a simple web-client link
and it is possible to embed the chat as well:
<iframe src="http://webchat.freenode.net?uio=MT1mYWxzZSYzPWZhbHNlJjk9dHJ1ZSYxMT00MQ41&channels=YOURCHANNEL" width="640" height="400"></iframe>If there is no need for an own channel, you can still talk about your project on related channels, like #freegamer or the channel of an engine that you use.