BookStack looks interesting, but certainly one massive advantage Retype has is just installation. I can have Retype installed, my website built, and running in a browser in a 10 seconds.

With Retype, your content source are simple Markdown `.md` text files. BookStack stores your data in a database, and in order to host a website you need a PHP webserver, Maria DB, etc.

A Retype generated website can be hosted for free using GitHub Pages. The retype.com website is hosted on GitHub Pages, see https://github.com/retypeapp/retype.

Hope this helps.