wp admin: is there an add-on to create multi-site WP installations programmatically?

So I created a multi-wordpress site and I want to be able to create multiple sites on the network programmatically. My subscription service has an API to be able to create usernames and passwords on the fly when they register. I just need to be able to create the site with some default values ​​when they register.

Also, if there is a good administration tool to manage these sites, it would be amazing.