Developers/Projects
Most developers will probably be working on an Activity for use on the OLPC. This kind of development can normally be done with little interaction with other development groups, save for the core Sugar developers (whose work directly affects activity developers).
Communications Channels
Most of the core developers use IRC for instant-messaging-style communications:
irc.freenode.net #sugar #olpc #olpc-content
the Sugar mailing list is also used for broader comment and collaboration:
List Information
If you have a large number of developers in a given area and would like to set up a local discussion list, post to the Sugar mailing list with a request for a new discussion list.
Current Active Local Discussion Lists:
Unofficial news and interesting tidbits often show up in the blog aggregator for the project.
Requests and Ideas for Projects
Software ideas describes activity and tool types that are currently needed. If you have an idea for an activity, add it to the list in the appropriate category (create a new category if necessary). You can create a new wiki page to describe your idea in more detail.
Existing Projects
Software projects describes the currently active projects that may need help. Once you have decided on a project, add yourself to the list along with your contact information, homepage (which may be a wiki page on the OLPC wiki), etceteras. In particular, the various Activities available on the XO may need help as build time draws near; if you're looking for an existing project to get your feet wet with, check there.
Available Resources
The Developers Program provides general project management facilities for OLPC projects.