Coincidentally, I've only been building for Windows, so different from the platforms supported by Rewind. If anyone wants to collaborate, I'd be very open to it.
Philosophically, I think almost everything we see and think about is in a web browser these days. Even private conversations with my friends, I often look up a few things about them. So I've been using irchiver myself to dogfood it, for almost 2 years now. And found it to be super useful already. For example, I've recovered important technical posts that someone deleted, paragraphs on text I lost when submitting a form that didn't save, or found a comic strip that I had at the tip of my tongue but got lost in google search.
And I think it's now possible because of strong+efficient screenshot compression and good OCR. There's an undocumented Win32 hack that lets you capture window content in a fast way (moreso that a typical BitBlt) so I used that to grab the images. And made a standard inverted index search engine for the content. Anyways, the webpage I put up for the project explains it as best as I can to a general audience [https://irchiver.com/].
In many ways, it's like the Rewind startup here. Except it just happens I did it for Windows, and they did it for MacOS and iPhone. And I care a lot about local storage of the original screenshots and text. Would love to hear others' thoughts.