You're talking about WURFL and Luca Passani. I recall working with it for a project 15 years ago.

https://en.wikipedia.org/wiki/WURFL

BTW: It looks like WURFL is still a thing. He seems to have made a business of it[0].

The key to WURFL was a massive XML file. That was constantly updated with the latest gizmos, and whatnot.

[0] https://www.scientiamobile.com

Yup. That's it.