XVier is a single-player implementation of Connect Four against the computer. You can test your planning skills against the computer in order to end up with four pieces lined up in a row. For anyone actually capable of defeating the default computer, command-line arguments exist to increase the difficulty until the computer plays a near-perfect game. The board size can also be adjusted.
If you were wondering where the name came from, Vier Gewinnt is the German name of the original board game. This version is written by Norbert Jung in 1992 and tested for an assortment of contemporary Unix machines such as the Sun4, IBM RS6000, DEC DS5400 or Sequent Symmetry, among others.
The following is a typical session, in which the computer wins. As expected.
XVier is still packaged in Debian and likely other distros too. You too can be soundly trounced by a computer in Connect Four.
More general information on old X games, including build tips can be found in the Old X Games article.
If the above video does not work for you, it is also available on my YouTube channel.