It's open source: https://github.com/magcius/noclip.website

I wouldn't say it emulates so much as implements a renderer for each game. It's totally nuts.

Yes! I loved the thread on twitter back in the day where Jasper explained how he implemented the Half-Life 2 water shader using the two camera method.

I can wholeheartedly recommend going through his account there and on bsky, lot's of interesting stuff.

I contributed one earlier this year! The community's a great bunch and I learned a lot.

Always remember, folks: the best feature request is a pull request ;)