You can compose a site from content blocks in Decap similar to how you'd do it with Advanced Custom Fields in WordPress, but you'll either need a theme created with that in mind or make your own theme. It's enough for lots of typical simple business websites.

https://tina.io/ is another open source CMS you can look at. You need to host the CMS part yourself or use their hosting (there's a free tier). I'd love more open source solutions like Decap that don't involve hosting anything and don't involve paid per-user subscriptions but I don't know of any.

Also, I've seen https://formspree.io/plans used HTML contact forms. 50 free submissions per month with simple integration.