Was it possibly integrated into Adobe ImageReady [0]? It had a feature like what you're describing where after you finished designing your website, you could define cutouts and export as images+HTML.

This is actually how I first got into programming when I was younger. I made my first site in ImageReady, but it couldn't do all the other cool stuff other sites did like comment sections and logging in, so I went on a quest to learn how to do all that and the rest is history :)

[0] https://en.m.wikipedia.org/wiki/Adobe_ImageReady

Edit: actually, I found an example from 13 years ago https://youtu.be/qCq0JiwMcJs