This morning at the Google I/O Developer Conference (San Francisco, May 27-28, 2009), Google launched a developer preview of a new communications platform called Wave 

Wave will be open source, rest on open standards (particularly HTML 5), and offer open APIs.  It’s an ambitious, versatile tool that will implicate OA primarily in the ways in which it supports document sharing and collaborative document writing. 

For an early review of Wave’s capabilities, see the article by Juan Carlos Perez in PC World or the article by MG Siegler in TechCrunch.

Also see the Wave "about" page, the Wave developer blog.

Update (5/29/09).  The 120 minute video demo of Wave wasn’t available yesterday but it’s available today.  Recommended.