Sharing Project Development Knowledge
To make software development work, everyone involved needs a good working knowledge of the product, the domain, the solution and so on. Communicating enough, but not too much, information can be tricky, especially in an agile environment where anything can change at any time.
Tarek Abdelmaguid has an interesting list of ways to communicate while working on a project. I have done almost all of them with various clients and employers, and also made a lot of use of instant messaging. There is definitely scope for using more structured communications such as mailing lists, internal blogs and forums, though.