http://ksi.cpsc.ucalgary.ca/KAW/KAW96/chen/kawchrono.html
This describes CHRONO, a tool for web servers to automatically note which
pages on the web site have changed, and present users a chronologically
sorted list of recently-changed pages. There is also something called
Meta-CHRONO which maintains similar information across disparate sites.
However I think the sites have to be running CHRONO.
http://www.netmind.com/URL-minder/URL-minder.html
This is a server which lets you enter a list of URL's and your email
address, and it will send you email when any of the URL's change. It
is an offshoot of the "netminder" service which will send you reminders
about birthdays, anniversaries, etc. that you can specify. No privacy
here, but otherwise this could be a pretty convenient way to track your
favorite sites.
http://www.specter.com/sb30menu.html
This is a commercial program called Surfbot which sounds like it has some
relevant features. It can download web pages to your local computer during
the night, do some searches on its own, check when your bookmarks need
to be updated, etc. I'm not sure whether it can just make a list of
changed sites, or whether it actually downloads copies of the changed
sites to your computer. A free demo version is available, but I haven't
had a chance to look into it in more detail.
http://www.vuw.ac.nz/~newbery/Katipo.html
This is a Mac-only program. It looks at the history file left by your
web browser, and goes out and checks each page you've visited recently
to see if it has changed. It doesn't have to download the whole page,
it just asks the server for the "Last-Modified" time, so it is supposed
to put relatively little load on the web. (I don't know whether the
other programs on the list also use this method.) It's a little strange
that it does this on the history file rather than the bookmark file; the
author promises to add this kind of enhancement someday.
For now I have put a few sample pages into the netminder URL watcher.
I'll see if it works.
Hal