Eleventy: https://www.11ty.dev/​
Eleventy Authors demo using On-demand Builders: https://www.11ty.dev/authors/ (URL updated: July 29, 2022)

Netlify’s On-demand Builders: https://www.netlify.com/blog/2021/04/14/faster-builds-for-large-sites-on-netlify-with-on-demand-builders-now-in-early-access/