Step by step playback draws a cheer

Let's say you are added to a conversation (a wave) that has been going on for a long time? You can be added at any relevant point, not just the end. But even cooler, you can do a playback of the entire evolution of the conversation.

But wait: there's more! Let's say you want to edit your message (or even a message that was written by another participant in the wave). Yes, you can. The original author is notified, but every participant can see that the message has been modified, and if they want, can replay the changes.

This leads to a change in behavior: conversations become shared documents. The screenshot below shows a simple example, as Gregory and Casey collaborate to produce a good answer to Dan's question. As Stephanie Hannon, the product manager for Googe Wave, said to me, "In Wave, you don't have to make the choice between discussing and collaborating."

As anyone who's used version control knows, a document with lots of discussion and edits can become pretty messy. No problem. You can export an edited wave as a new wave, and start over. "One of our design principles," says Lars, "is that the product of a wave can be as important as the original wave."

Nor do you need to include everyone in every part of a conversation. Essentially, Lars, says, "waves are tree-shaped sets of messages. You can shape a subtree, or a sub-conversation and limit the set of participants in any way you like."