Google Wave is a real-time communication platform. It combines aspects of email, instant messaging, wikis, web chat, social networking, and project management to build one elegant, in-browser communication client. You can bring a group of friends or business partners together to discuss how your day has been or share files. Some are the features of Google Wave are, it is Real-time, Open source, etc.
The main idea behind Google wave is instead of sending a message along with its entire thread of previous messages, requiring all responses to be stored in each user's inbox for context, message documents (called as waves) that contain complete threads of multimedia messages (blips) are perpetually stored on a central server. Google Wave provides federation using an extension of XMPP (Extensible Messaging and Presence Protocol), the open Wave Federation Protocol. Being an open protocol, anyone can use it to build a custom Wave system and become a wave provider
Google Wave is a communication system, just like email or instant messaging. Only it combines these methods of communicating and adds a few more. Google Wave allows you to see messages near instantaneously as you type, but it also allows people who aren't logged in to join the conversation later.
Google is building APIs that allow developers to use and build on Google Wave like extensions, program robots to automate common tasks and/or build gadgets to extend or change user interaction (e.g., posting blips on microblog feeds). Google wave Extensions are mainly of 2 types:
Gadgets : A gadget is an application users can participate with, many of which are built on Google's OpenSocial platform. A good comparison would be iGoogle gadgets or Facebook applications.
Robots : Robots are automated participants within a wave. They can talk with users and interact with waves. They can provide information from outside sources (i.e. Twitter, stock quotes, etc.)