Google Wave

As a re-invented take on e-mail, Google created Google Wave, which is an open-source platform that combines e-mail with instant messaging and real-time collaboration of documents and images.Official Site: About Google Wave
The new feature was introduced at the Google I/O Conference in San Francisco, California, on May 28, 2009. While the platform was only opened to select developers at the time of the announcement, users looking for a first look at the new feature can apply to receive updates and access.Official Site: About Google Wave
How It Works

Users come together on Google Wave in an application similar to an instant messaging service. In a real-time setting, users can then collaborate with other users, add and edit images, videos, maps and text documents. Each wave is logged, so users can playback the conversation or view older versions.Official Google Blog: Went Walkabout. Brought back Google Wave.
The goal was to merge different types of communication, e-mail, chat and documents, into a single communications model. Google Wave also provides open APIs, allowing developers to embed waves to their sites as well as build new applications to work within the platform. Additionally, Google Wave provides natural language tools to integrate contextual suggestions and assistance with spelling.Official Google Blog: Went Walkabout. Brought back Google Wave.