[NB since version 2.1.0, we have had to make a slight change to the name, its full title is now Website Watchman.]
It has been a (deliberately) long road but Watchman for Mac now has its first commercial release.
So what does it do? In a few words. "Monitor and archive a website".
There are apps that monitor a url and alert you to changes. There are apps that scan an entire website and archive it.
Watchman can scan a single page, part of a website or a whole website. It can do this on schedule - hourly, daily, weekly, monthly. It can alert you to changes. It builds a web archive which you can view (using Watchman itself or the free 'WebArchive Viewer' which is included in the dmg). You can browse the urls that it has scanned, and for each, view how that page looked on a particular day.
We're not talking about screenshots but a 'living' copy of the page. Watchman looks for and archives changes in every file, html, css, js and other linked files such as pdfs. You can obviously export that page as a screenshot or a collection of the files making up that page, as they stood on that date.
A 'must have' for every website owner?
Try Watchman for free / buy at the introductory price.