Glest, being open source, is available for many Operating Systems, and since no one operating system works the same, it's necessary to use different methods to get Glest for your operating system.
Before download glest, you should consider that it's developed has stopped in april 2009. There are two projects which continue and have added lots of features, factions and maps since then. Glest Advanced Engine is especially known for offering a richer single player experience, MegaGlest for better and more stable online-gaming.
The easiest way is to download the installer from Sourceforge.
Cider House has a complete Mac OS X Glest 3.21 package and installation guide.
There is a patch to port Glest V2.0.0 to FreeBSD on the FreeBSD webpage
Also see Compiling Megaglest for FreeBSD
This is the easiest way to install Glest. Open the package manager of your distribution (f.e. synaptic package manager, Kpackage manager, yast, ...), search for Glest, and install it.
Or on ubuntu or debian: open a terminal and type: "sudo apt-get install glest" enter your sudo password, and Glest will be installed.
Pbone.net has RPMs for Suse, Mandrake, Mandriva, PCLinuxOS, and FedoraCore.
Download from the Sourceforge page or SVN (see below).
Use Kdesvn to checkout the Glest code. Windows users can use TortoiseSVN.
- Go to the Subversion menu -> General -> Checkout a repository" and enter the URL: 
- Select a directory to put the files in.
Command Line method:
- Go to the directory, on the console, where you want the files.
- Enter "svn co https://glest.svn.sourceforge.net/svnroot/glest glest" (make sure SVN is installed).
For more information on SVN see the SVN Reference.