How to fix problems with your local development environment
There are many local development environments for WordPress out there, including XAMPP, MAMP, LocalWP, Lando, and DevKinsta.
Recommendations
I always recommend LocalWP and Lando. They come with all requirements by default, and you don't need any SSH skills to install missing packages or customize your configuration.
Problems with LocalWP
When using LocalWP on Windows you should avoid setting the webserver type to "NGINX" because what you get isn't just an NGINX server, but a reverse proxy setup including NGINX and Apache.
This hides the original IP from your WordPress installation and causes the "Can't make requests to itself" error in our diagnostics.
Problems with XAMPP and MAMP
While XAMPP and MAMP are usually great tools for local WordPress development, they lack support for some critical PHP, and WP features to work seamlessly with Simply Static.
One thing is the support for WP-CRON. WP-Cron is optional in Simply Static, but you will need it if you like to convert larger websites with Simply Static—if not, your web server will time out after at least 30 seconds.
Problems with DevKinsta
While DevKinsta is relatively new and looks fancy, it gets even worse regarding supported features. There is no WP-Cron configured in DevKinsta, and they don't ship cURL support (a PHP package for making remote requests). Without cURL, you can't use Simply Static at all.
Problems with SSL
Simply Static needs an SSL certificate in place to export your website correctly. It's also required to communicate with the GitHub API; otherwise, it will reject all requests from WordPress.
You can use self-signed certificates for that purpose which most local development tools provide with a One-Click-Solution.
Diagnostics
You can quickly check if your local development tool provides all the necessary extensions and features to get the most out of Simply Static by checking Simply Static -> Settings-> Diagnostics. Here is a screenshot from a local website running on LocalWP:
WordPress Playground and Studio (from Automattic)
We are already working on making Simply Static compatible with both Playground and Studio.
We can't recommend them right now because they lack the ability to use cURL in PHP, which is needed to fetch pages and files from your website.
However, as both of these projects are under heavy development, we expect to have compatibility soon.