How are GNU/Linux users preparing for Linus Torvalds' plan of world domination? By playing free software computer games based on the classic world conquest board game Risk. You can perfect your strategy by playing the games XFrisk, TEG, or Ksirk.
XFrisk uses the X toolkit (Xt), which was popular 15 years ago. XFrisk itself isn't that old, but it shows the maturity of a classic X application, and most major GNU/Linux distributions include it in their default repositories. You can also download source code from XFrisk's download page.