It was open sourced as Apache Wave when Google shut it down.

Years later Apache moved it to read only because of low community activity.

The archived git repo on GitHub remains available to clone and revive as a fork.

https://github.com/apache/incubator-retired-wave

This was the first big secret “you’re not allowed to know what this is or talk to anyone about it” project inside Google. They wanted to be left alone and especially to not have to integrate with the mail team. And everyone heard rumors of gigantic bonuses if they hit whatever milestones, which wasn’t a thing for other projects. All this made them isolated within the company, and when the project was an obvious flop, you didn’t see anyone rushing over to help them.

Notion pages are pretty good for shared trip planning docs. Although maybe without so many live updating widgets.