What's this site built with?

This website is built with Jekyll and hosted on gitlab pages for FREE.

Jekyll is a static site generator, an open-source tool for creating simple yet powerful websites of all shapes and sizes. From the project's readme:

Jekyll is a simple, blog aware, static site generator. It takes a template directory [...] and spits out a complete, static website suitable for serving with Apache or your favorite web server. This is also the engine behind GitHub Pages, which you can use to host your project’s page or blog right here from GitHub.

Gitlab Pages is a great way to host static websites for free. The site is published directly from a repository in GitLab using continuous integration.