Not A Blog is a WordPress plugin to use when you're using WordPress solely as a CMS to power a custom plugin.
It disables the front-end (redirecting to a chosen wp-admin page) and removes the blogging menu items from wp-admin.
Before/After Not A Blog:
Blogging-specific submenu items are also removed.
To define which page from your plugin should be the default landing page, return the URL from the not_a_blog_default_page filter, like so:
add_filter( 'not_a_blog_default_page', function ( $url ) {
return 'wp-admin/admin.php?page=my_custom_page';
} );
This code should live in your plugin (or in some separate plugin, just not in Not A Blog).