Key features of Kolibri: simple GUI, small footprint, integrated PHP support, customizable logging functionality, supports get, head, and post, configuration can be changed at the run time, run multiple instances with different document root settings, portable, can be put on USB stick and run without any installation, and viable alternative when already servers, like Apache or IIS are overkill. Kolibri+ is primarily intended for testing, development and demo activities as well as delivering Web site on a CD types of applications. It is also a good choice for someone starting web development and PHP. It is probably the simplest Web server for PHP development (at least on Windows).
Kolibri+ is not intended for any serious production use. Version provided here is MSI installer, you can download no-installation zip file from author's Web site. This version is the first release on CNET Download.com.