You can apply at the Wave page, so you don’t really need an invitation.

I had used the Google wave and pleased to say that yes it can replace the way of Email and Chat.

Every things has got some pros and cons …

But it is still available though the invitation, It must be given to all.

Thanks for details study.

@Southern Highlands real estate:In reality, Wave is no less private than email. If someone just forwards the email to another party, all the email addresses in that email get forwarded also.
Still, it would be nice to be able to limit who can add participants to a Wave.
Perhaps I was not clear enough. A Wave acts as both an email and a chat. It’s hard a bit hard to explain unless you try it for a while and see what it can do. One of the basic extensions is Google Maps. If one person in the Wave moves the map, everyone else on the Wave sees it in real time.

You have wrote a great review on Google Wave. It is new information for me. I never heard about it till now. I agree with you, it could replace typical chat programs because the features you wrote is simply great. But i think Google Wave should provide privacy to add people to your thread or email.