One feature SSGs are missing is email contact forms. Some of them use Netlify forms https://www.netlify.com/platform/core/forms/ - 100 submissions per site /month ($19+ when exceeded). https://docs.netlify.com/accounts-and-billing/billing-faq/
Hugo's Piko theme uses FormSubmit.io (free) or Fabform.io ($5/mo). But I haven't tested that to understand how well it works and why/how it's free.
Hugo's Tella theme uses getform.io -- https://github.com/opera7133/tella/issues/63 (50/mo).
250/mo for free and $8/mo for unlimited with https://web3forms.com/ is the best I've seen so far _(besides the completely free one which I'm not sure about)_.
I haven't seen any of them mention using an SMTP.
I saw these *HTML templates* https://html5up.net/ recommended on another forum, but I would think they’d require more technical knowledge to use/customize than an SSG. They’re all pretty elaborate too. None are basic business or personal type websites.
# Wordpress:
I created a basic, free WordPress site some years ago when I was trying to set up a blog and I found it difficult to use and opted instead for Blogspot. However, I have more experience & knowledge now, so self-hosted Wordpress might be an option.
When I looked into Wordpress I was comparing the ".com" options (wordpress.com/pricing) with Squarespace, and they were more expensive. Now that I'm more familiar with hosting my own linux web server, I could probably use the ".org" and host on a $5-10/mo server but *I get a lot of traffic on my business site (_can reach 1m+ views in a month_) and I'm not sure how good/costly a server I'd need to keep it running*.
I saw *Oxygen Builder* recommended as a "Squarespace-type UI" for Wordpress, and I watched some of the tutorials (oxygenbuilder.com/tutorials) and it seems like a decent option for a one-time $130 fee. But still not static.
I saw someone using the https://generatepress.com/ WordPress theme for their website https://servermanager.guide/about. It looks like the premium $44/yr option may be similar enough to Squarespace.
It looks like you can also install wordpress on your PC and use plugins to output static sites. A limiting factor may be finding free/cheap plugins that make it as easy to edit as Squarespace. And I don't see a way to get contact/email forms working.
# Flat CMS options:
I found this [10 Best Flat CMS for Lightweight Websites - https://www.hongkiat.com/blog/flat-cms/] which lists *Grav* at #1. I checked out Grav and it's purely markdown and has nice templates (_Open Publishing Space, Agency, Deliver Site_) https://getgrav.org/downloads/skeletons. So that might be the best option. The Agency template has a *contact form*, but [looking at the code](https://github.com/getgrav/grav-skeleton-agency-site/blob/de...) I don't see how it's being submitted/sent/emailed.
I found this page - https://learn.getgrav.org/17/forms/forms/example-form - which looks like it can utilize any SMTP - https://github.com/getgrav/grav-plugin-email/blob/develop/RE.... But that, the installation instructions, and [the webhosting section](https://learn.getgrav.org/16/webservers-hosting) all indicate that it's not a static site that you can upload to Netlify. But it still seems like a cheap and user-friendly alternative to Squarespace.
It looks like Grav has a [static generator plugin](https://getgrav.org/downloads/plugins) (and another one called [blackhole](https://github.com/barryanders/grav-plugin-blackhole)). If you can install php on your PC you can probably use Grav locally to output a static site. I'm guessing that would disable the email/contact function (and other dynamic features) though.
I saw [*Decap CMS*](https://decapcms.org/) mentioned as another possibility but the editor seems too limited.
It looks like the other "Best Flat CMS" options are also not static sites.