Software

Client Of Win (COW)
Features client documentation and download, game information, and settings.
http://cow.netrek.org/

Continuum Software Library
Check out the section 'blessed clients' for a list of many clients for different platforms.
http://www.continuum.real-time.com/software.html

JTrek
A Java Netrek client - Beta
http://www.starwave.com/people/robertt/JTrek/

Netrek Vanilla Server
Here you can get the latest source of the Vanilla Netrek Server. (NB: to play you don't need the server, just a client for your platform).
http://vanilla.us.netrek.org/

Paradise Netrek Development
Server and client sources.
http://paradise.netrek.org/develop.html