Not as big as some of the examples here, but still kind of interesting. I worked for a city government, and the entire backend code for our work-bids site was a few hundred files of PHP written with some sort of Dreamweaver framework that was deprecated years ago. Old enough that the entire site had to be run on PHP 5.7. I ended up rewriting the entire thing with Laravel (the framework of choice for the other webdev that was in the IT dept). It really didn't take that long; he just had too much on his plate to worry about it before I showed up.