A first draft for a script, which converts a Kirby site into a static site. It's a rough first draft, so don't expect it to be perfect. Play with it, if you like it!

statify.php

<?php

/**
 * Instructions:
 *
 * 1. Put this into the document root of your Kirby site
 * 2. Make sure to setup the base url for your site correctly
 * 3. Run this script with `php statify.php` or open it in your browser
 * 4. Upload all files and folders from static to your server
 * 5. Test your site
 */

// Setup the base url for your site here
$url = 'http://localhost/kirby/support/starterkit/static';

// Don't touch below here
define('DS', DIRECTORY_SEPARATOR);

// load the cms bootstrapper
include(__DIR__ . DS . 'kirby' . DS . 'bootstrap.php');

$kirby = kirby();
$kirby->urls->index = $url; 

$site = $kirby->site();

if($site->multilang()) {
  die('Multilanguage sites are not supported');
}

dir::copy(__DIR__ . DS . 'assets',  __DIR__ . DS . 'static' . DS . 'assets');
dir::copy(__DIR__ . DS . 'content', __DIR__ . DS . 'static' . DS . 'content');

// set the timezone for all date functions
date_default_timezone_set($kirby->options['timezone']);

// load all extensions
$kirby->extensions();

// load all plugins
$kirby->plugins();

// load all models
$kirby->models();

// load all language variables
$kirby->localize();

foreach($site->index() as $page) {
  $site->visit($page->uri());
  $html = $kirby->render($page);

  if($page->isHomePage()) {
    $root = __DIR__ . DS . 'static' . DS . 'index.html';
  } else {
    $root = __DIR__ . DS . 'static' . DS . $page->uri() . DS . 'index.html';
  }

  f::write($root, $html);

}

?>

Your site has been exported to the <b>static</b> folder.<br />
Copy all sites and folders from there and upload them to your server.<br />
Make sure the main URL is correct: <b><?php echo $url ?></b>

This is super helpful, thank you!
One issue though is that the links it generates are relative rather than absolute. So the link to the about page is /about rather than http://staticsite.com/about.

Is this intended behaviour? And is there a way to stop this happening?

Many thanks.