This is a super simple app that tracks weight, daily–if you wish.
Its been through many iterations over the years, mostly to experiment with different technologies. In the current form, it's a handful of HTML pages with PHP. Very basic.
A simple database table is required. A script for MySQL is included in this repo, but other relational database systems will work too.
A config.php file is required. An example is included. Rename config-example.php to config.php and set the database parameters as needed. See PHP PDO::__construct for a through explanation of the data source name.
There's a simple username/password scheme here. Set them both along with your server's domain in the config file. Logins are saved as cookies for 90 days.