The nuts and bolts of AirPrint are CUPS (linux printer server) plus Avahi (mDNS infrastructure, known in Apple land as Rendevous). My recollection is that to get my USB printer to AirPrint, I only needed to install the CUPS and Avahi packages, and then things magically worked. YMMV.

I have it running right now. My old school LaserJet 1320 is wireless on my home network. It's connected to a Raspberry Pi Zero W.

As someone mentioned, it's basically CUPS and Avahi. I've set it up years ago and it just runs.

The only thing that sucks is that printing from an iPhone takes about 5 minutes because of all the processing on the RPi. I suppose using a higher end RPi would fix that, but I like the small form factor. Printing from a PC is instant.

Does anyone know of any similar magic for turning an RPi into a Chromecast?

Air print is really easy. It’s built into Utunu printer sharing. https://askubuntu.com/questions/26130/how-can-share-my-print...

There is a very similar level of magic for converting a raspberry pi to do AirPrint

https://github.com/willswire/balenaPrint

I was able to do this on Ubuntu 16.04 with CUPS. It was surprisingly easy. I just googled and followed some guide on the first page of results.