We're talking about servers here - the article specifically said that one of the requirements was no special _server_ software, and a web server almost certainly has zip (or tar) installed. These gwtar files don't work without a server apparently either.

I'm not following your point here. Yes, a web server (probably) has access to zip/tar utilities, but so what? That doesn't automagically make a random .zip jump through hoops to achieve anything beyond 'download like a normal binary asset'. That's what a ZIP file does. Meanwhile, Gwtar works with any server out of the box: it is just a HTML file using a pre-existing HTTP standardized functionality, and works even if the server declines to support range requests for some wacky reason like undocumented Cloudflare bugs, and downgrades RANGE to GET. (It just loses efficiency, but it still works, you know, in the way that a random .zip file doesn't work at all as a web page.) You can upload a Gwtar to any HTTP server or similar thing like an AWS bucket and it will at least work, zero configuration or plugins or additional executables or scripting.

Now, maybe you mean something like, 'a web server could additionally run some special CGI software or a plugin or do some fancy Lua scripting in order to munge a ZIP and split it up on the fly so as to do something like serve it to clients as a regular efficient multi-file HTML page'. Sure. I already cover that in the writeup, as we seriously considered this and got as far as writing a Lua nginx script to support special range requests. But then... it's not single-file. It's multi-file - whatever the additional special config file, script, plugin, or executable is.