This is a lightweight alternative to TGM Plugin Activation class, which is currently the best way to require and recommend plugins for WordPress themes (and other plugins), according to the TGMPA homepage.
My code is smaller and more concise, while being extendable and customisable from a design point of view.

Here’s the main function:
<?php
function supernova_register_required_plugins($pluginArray) {
$action = 'install-plugin';
foreach ($pluginArray as $recommendedPlugin) {
$name = $recommendedPlugin['name'];
$slug = $recommendedPlugin['slug'];
$file = $recommendedPlugin['file'];
$link = wp_nonce_url(
add_query_arg([
'action' => $action,
'plugin' => $slug
],
admin_url('update.php')),
$action . '_' . $slug
);
$status = ' (not installed)';
$buttonStatus = '';
if (file_exists(WP_PLUGIN_DIR . '/' . $file)) {
$status = (is_plugin_active($file)) ? ' (active)' : ' (inactive)';
$buttonStatus = (is_plugin_active($file)) ? 'button-active' : 'button-inactive';
}
echo '<a href="' . $link . '" class="button button-secondary ' . $buttonStatus . '">' . $name . $status . '</a> ';
}
}
?>
And here’s the function call inside your plugin or theme settings panel:
<?php
$recommendedPlugins = [
[
'name' => 'Yoast SEO',
'slug' => 'wordpress-seo',
'file' => 'wordpress-seo/wp-seo.php'
],
[
'name' => 'CMS Tree Page View',
'slug' => 'cms-tree-page-view',
'file' => 'cms-tree-page-view/index.php'
],
[
'name' => 'Intuitive Custom Post Order',
'slug' => 'intuitive-custom-post-order',
'file' => 'intuitive-custom-post-order/intuitive-custom-post-order.php'
]
];
supernova_register_required_plugins($recommendedPlugins);
?>
I might revisit the code later to make it more modular and more functional (as in Functional Programming) codewise.

Technical SEO Specialist, JavaScript Programmer and Senior Full Stack Developer. On a quest to experiment with Canvas, WebGL, JavaScript, SEO and WordPress, among many other things. Founder of WPDublin and SpeedFactor, co-organizer of Dublin WordPress Meetup group.
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Hey,
Thanks for a great alternative to the TGM Plugin.
Is there a way to include external plugins too?
Many thanks,
Paul
You would probably need to fetch and unzip them from any external source, such as a URL, a bundled plugin or a public GitHub repository.
Maybe with the upcoming changes to WordPress bening able to update plugins from non-WordPress.org locations, it might work out of the box with minimal code changes.