You may be talking about iodine: https://code.kryo.se/iodine/

You can host it yourself.

Unrelated comment: I like this sort of web design. Might just be nostalgia. It reminds me of web design circa 2001 or so. You can see many similar examples on OSWD, e.g.:

http://www.oswd.org/design/preview/id/9/

http://www.oswd.org/design/preview/id/3/

http://www.oswd.org/design/preview/id/6/

http://www.oswd.org/design/preview/id/45/

At some point I had a binary for the iodine client stored as DNS records, and another DNS record with a shell script that would fetch and decode them.

That's well known in exfiltration botnets.

I read about it years ago. Someone used a free Microsoft internet connection to activate their Windows.

The connection only allowed access to MS activation servers, but also DNS.

The DNS would resolve any domain, even the ones that don't belonged to MS, so they could use it to get data out.

I told this story to a few people in my time, all working in IT, and all thought I was bullshitting them, like I was some crazy conspiracy theorist.

And now I'm reading that this is a well known technique and there are even libraries doing this.