Today Wave is still in active development, but Google are confident that enough of the rough edges have been knocked off and are making it available to all:
Starting today, we are making Google Wave openly available to everyone as part of Google Labs. You no longer need an invitation to wave — simply visit wave.google.com and sign right in. Likewise, if you are a Google Apps administrator at a business, school or organization, you can now easily enable Google Wave for all your users at no extra cost (more on ourEnterprise blog).
In the announcement made on the official Google Wave Blog they highlight how some educational institutions are already using Wave:
University students and professors worldwide have used waves within and beyond the classroom to collaborate on Latin poetry translations, write academic research papersand even build new functionality with Wave’s APIs. An ICT teacher also enjoyed having her 5th-graders do their class research in Wave.