According to links I found on the page, it looks like the software being used is provided by Kiwix [1], and the file format used to archive Wikipedia (and other sites Kiwix archives) is ZIM [2].

I agree, it's an interesting project. I would like to see more specifically about how many users they can serve at once from a Pi Zero. Unless they just stuck Cloudflare in front of it?

[1] https://www.kiwix.org/en/

[2] https://openzim.org

Hi, Yes this was a very simple project. Basically I had a raspberry pi zero w , installed apache and setup a virtual host that forwards all request to a another back end. Basically the Kiwix software that serves the wikipedia Zim file runs on port 8080. The raspberry pi has a 32 gig card and not enough space to host the 82 gigs of the wikipedia zim file. I had a spare external drive that I formatted in ext4. Originally the drive was formatted as extended FAT32 but the raspberry pi showed a lot of high CPU when accessing the Fat32 partition. I formatted it to ext4 and mounted the volume and downloaded the wikipedia zim file. Then I created an index file for Kiwix server and, started the Kiwix server and restarted apache had wikipedia running on a raspberry pi zero w. It did crash, I was thinking of adding cloud front as I have a free AWS account but I haven't got to it yet :)

There are different dumps. Text doesn't take much space. It's the images and videos. Usually about a 100GB. Check https://wiki.kiwix.org/wiki/Content_in_all_languages