As an avid Calvin and Hobbes fan in my youth, I often found myself looking up YouTube videos and websites of the strip. I want to say this was around the late 2000's. As a kid I used to frequent this website, if I had to guess the name of it it was probably something like calvinandhobbes.com or something of that realm. The main reason why I visited this site in particular is because of the forum-like custom comic hub that was hosted there.
Essentially, you could add text to whited-out speech bubbles that already existed in the panels, if that makes sense. You could juxtapose any panel from any point in the strip's history to tell your own stories. It even supported YouTube link embeds.
After some time of not visiting the site I ended up checking it out again some time in the early 2010's to find out that the site wouldn't connect, like there were issues with something technical on their end.
If anyone has any questions about it I'd love to answer them, to the best of my ability of course. Thanks in advance for reading this if you did!