CrushFTP supports allowing users to self register on your server.  This is not automatic, and you must configure and personalize this experience.  You have extensive controls over the entire process.

The first step is to create a username in the user manager that will be used for this.  Keep it simple, and use a basic simple password too.  Do not assign them any additional privileges as this will be a public account that is used for doing registrations.

I suggest an account name "register" with a password of "register".  This will allow you to use a URL like this to reach the registration page:

https://www.crushftp.com/?u=register&p=register&path=/WebInterface/jQuery/messageForm.html

When this page loads, it looks at the URL to see the name of the HTML file.  The default is "messageForm" and its fine to keep it this way.  It then asks the server to give it the registration form named "messageForm" as long as it has been assigned to the "register" user.  If it hasn't, you will just get a blank page.