It’s a demo of an “external core” style Feather Wiki on Tiddlyhost. Click the link above for more info, and to try it out for yourself.
A brand new empty is 714 bytes. It does grow as you add your content though.
One question to ponder for TiddlyWiki hackers (making sure this is on topic… ) - An external core TiddlyWiki is still 107 KB. Could it be smaller? How and/or why not?
In @cdruan’s html, I don’t see $:/boot/boot.js, so that must be externalized as well. Probably that is the reason for the size difference. I didn’t look into the details to see how tw-external-js accomplishes this.