FreeCol

  Web Link
  Link   Development Site
Our development site at SourceForge.net.
  Link   Code Mirror
Our code mirror on GitHub, including Nightly Releases.

Colonization

  Web Link
  Link   Sid Meier's Civilization IV: Colonization
The official re-imagining of Colonization, released in 2008.
  Link   Unofficial Colonization Home Page
A site dedicated to Colonization.

Colonization Clones

  Web Link
  Link   The New World
A project aimed at making a real-time strategy version of Colonization.
  Link   Open Colonization
The project seem to have halted right after they launched their website in 2004.
  Link   NewCol
From their website: "The goal of this project is to let students learn computer science and C language in a funny motivating project."
 
  Link   Free Conquest & Colonization of America
A project using C and Ruby.
  Link   jColonization
Another clone that doesn't seem to have produced anything beyond a website and some screenshots. Neither code nor binaries have been published, making it likely that the screenshots are just mockups.
  Link   Colonization too
Using C++ this project was redesigning the game while implementing it. The project has unfortunately died.

Related Games

  Web Link
  Link   FreeCiv
An Open Source implementation of Civilization.
  Link   The Battle for Wesnoth
A turn-based strategy game with a fantasy theme.