Native PHP installers

By native PHP installer I think you mean a standalone version right? I have created such an alternative installer for Wordpress. I would upload that single file to an empty (sub)domain and access it thourgh the browser. The script will download latest version of WP, setup the database, installs a handfull of plugins we always use, create a user for everyone in my office and removes some default dummy Posts. Pretty handy and save some time on every WP project we (have to) do.

For Codeigniter projects I have included an installer directory to my setup. It's not native PHP as in a standalone file, but it's basicly a small CI project. The index.php referes to the same CI system folder as the real project so the installer project is just a handfull of controllers, models and views. The installer modifies the required config files, imports .sql file, adds some company details of the client to the database, adds the users etc.
Since CI is my tool of choise I find it handier and easier to create the installer as a CI project as to a standalone script.

These installers enable me to delegate some work to less technical staffmembers.