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Try Wave for yourself!

Wave is a web application for real time communication and collaboration, designed to help you get things done with groups of people. 
Each wave is a live shared space on the web where people can work together with text, images, videos, maps and more!

Google Wave:

Haven't tested Google Wave yet? Well, you're missing what is believed by many (and certainly by us) to be the best piece of web technology since the invention of the Web itself! Despite the end of further development announced by Google, the website is still running - UPDATE: Google Wave will become "read-only" on January 31, 2012 and will be turned off on April 30, 2012. 

Google Wave

Apache Wave:

The open source Wave code was donated to the Apache Software Foundation and Wave development now happens at Apache. The main project of Apache Wave is "Wave in a Box" (WiaB), a stand alone Wave server and rich web client that can serve as a Wave reference implementation. WiaB is still under development but, if you're feeling adventurous, you should test out the most advanced demo server:

Wave in a Box

Walkaround - Wave on App Engine:

Walkaround is a variant of Wave, based on the Apache Wave code base, that runs on App Engine. Walkaround can import waves from to allow users to keep working with their data regardless of the future of (The import feature is still experimental.)

Walkaround supports live concurrent rich-text editing, diff-on-open, in-line replies, user avatars, wave gadgets, attachments, and the team is working on integrating App Engine's full text search service. For now, it does not support Wave robots, extensions, federation, private replies, or archiving and folder management, but these features could be added. See the feature roadmap.

Try one of the DemoInstances, check out the code, or join the developer mailing list.

Google Code

Wave-Watchers' recommended Walkaround demo server: 
Walkaround demo server

Google Wave Alternative Solutions: 

This slideshow was accurate at the time of its first publication in april 2012.