Spatially enabled web app development environment.
It's important to note, however, that MapServer alone isn't a full featured GIS system. Instead, it's a tool that can be used to enable spatial data in your applications, making them more powerful and effective. If you're looking for a complete GIS system, you might need to look elsewhere.
One of the benefits of MapServer is that it's highly customizable, so you can tailor it to your specific needs. And if you're using a Mac operating system, the MapServer OS X package by Server Logistics is an excellent choice. This package includes the core MapServer software in an easy-to-install Mac installer package, as well as various support libraries, PHP/MapScript, Perl MapScript, and a version of the PostgreSQL 7.2.4 database with the PostGIS 0.7.3 libraries.
Ultimately, if you're looking for a useful tool to help you build powerful GIS web applications, MapServer is worth checking out. And if you're a Mac user, the MapServer OS X package by Server Logistics makes it easy to get started with this useful software.