Let me intro both of them a little. In DK old version distribution page they says the following-
Later they developed a web based games called 'Scourge' using this engine.The Dragon Knight game engine is an online game system created by Jamin Seven. It is an RPG-style game in which characters explore the map, fight monsters, gain experience and buy items, among other things. It is written in PHP4, with a MySQL database backend. While it was originally envisioned as a medieval/fantasy type game (think back to the NES game, Dragon Warrior, to which this game is a tribute), it is possible to make it into any other kind of game you want (space, modern, whatever). All statistics are handled by the database, so all items, monsters, etc., are fully customizable. It includes an administrative control panel suited for basic editing tasks, however, the best way to make large-scale changes are with a more comprehensive database tool such as phpMyAdmin.The game is released as a free program, with some limitations: You may install the game on your server and run it however you wish. You may also modify the program code for your own personal use in any way you see fit. You may not, however, redistribute the program (modified or stock) in any manner. And you may not alter the copyright or powered by notices at the bottom of the game pages in any manner. Short of those few rules, you are given free reign to do what you wish.Being a free product, no technical support is guaranteed - however, you are free to post on the official DK forums if you need help with something. Due to time restraints, I will not answer support requests via email, so don't even try. By downloading the game, you agree to the above-mentioned rules, and you also agree not to hold the author responsible for anything in the event that something goes wrong. You use this program entirely at your own risk. Once you agree to that, you are free to continue to the Downloads section below.Current version: 1.1.11
Gamers Fusion engine was another very popular game engine developed using PHP. As they stop giving support it's tough to get the source anymore. I'll come up with a brief description about that later.
Vallheru is another good turn based, web-browser, fantasy MMORPG written in PHP and MySQL including some other database support as well. It used Smarty Template Engine, ADOdb and PHP Mailer. Based on Gamers-Fusion ver 2.5 with many modifications in security, speed and features.
You can still download Vallheru from here http://sourceforge.net/projects/vallheru/ also has a lunchpad here https://launchpad.net/vallheru
We will discuss more games engine and stuff which developed using PHP later. Bye for now, have a nice day :)