I am planning on building a website that I will sell usernames and passwords to a password protected part of the site, but I want it so only 1 person can be logged into a same username at a time (which should eliminate password sharing violations to an extent).

If you know of any free php scripts that would do this post them below.

I would like the script to be a basic username and password php login script tied to a mySQL datebase that holds the usernames and passwords.

Check out scripts on sites like www.hotscripts.com or www.phpclasses.org

It sounds like to me that you would have to custom build this feature yourself, however, it would be pretty simple to create if you have any php experience.

Yeah i already went though hotscripts.com and found the script X-Protection (http://www.hotscripts.com/Detailed/44885.html), it has all i want except the "1 person can be logged into a same username at a time" feature. I can edit php scripts and combine some, but i have no clue how to program that feature straight up.

Know of any scripts that have any type of feature like this, or any sites that have code snippets close to this feature?

That would only take like 5 minutes in PHP/MYSQL if you know what your doing. All you need to do is set up a database:

user_id (autoincrement)
user_name
user_password
user_logged (0=no | 1=yes)

Then have a login script, and check to see if the user_logged value is 0 or 1, and allow them access accordingly.