I feel like a simple automatic capture of timestamp + url + screenshot would already be very useful. This gives you a visual memory of the things you've seen on the web. I've wanted to develop this for a while, as a browser plugin.

Being able to skim the past month or two click around the thumbnails would already be amazing. I've wanted to do that many times before to check if my memory was correct, or if a page changed since I last saw it, or figure out when I last saw something online.

You don't need a special viewer for it, as your operating system's file explorer can view the screenshots already, and you don't need to set up a crawl. Screenshots also compress well, as webp or png after crunching it.