AOLserver was way ahead of its time as it was a multithreaded server with native database connection to Oracle and PostgreSQL (as far back as 6.9). Its performance and ease of development was miles ahead of Apache and most other tools.
Zipcar was a Boston company that was founded around the same time in the same milieu as Arsidigita and adopted AOLserver since it provided such incredible performance.
I'm a bit surprised they ran it for so long but it makes sense. Many of the concepts that made it so compelling at the time remain quite relevant today though the advances in all areas of HW and SW make things like ORM less of a bear than they were those days.
It was a bear to maintain large codebases with. AOLserver could have won had move languages been built into the server (python, perl, etc) but Tcl was so well integrated trying to bring another language to its level would have been far too much work
It's an absolute delight to see this at the top of HN! I spent a good 8 years trying to convince people to use AOLserver over Zope as part of OpenACS (https://openacs.org).
AOLserver is still used in .LRN (https://dotlrn.org) which is why the GitHub repo is still alive.
You should check your contract to see what it says. In all likelihood, it is unreasonable to request royalties.