[tonyarkles]

While ITA no longer exists as a separate entity I don’t think, my understanding is that they pretty much wrote everything in Lisp.

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

https://franz.com/success/customer_apps/data_mining/itastory...

Grammarly too, although I don’t think it qualifies as a 20-year codebase: https://www.grammarly.com/blog/engineering/running-lisp-in-p...

[farray]

ITA started doing everything in Lisp, but especially as the original coding founder left, started hiring people doing stuff in Perl, Python, Ruby, Java, shell, C++, PL/SQL, etc.

The core software was still Common Lisp, but lots of cruft got added, and Conway's Law kicked in mightily.