A collection of 15+ years worth of fan-made improvements to the game we love in one big easy to install package. Just buy the game (http://www.gog.com/game/sid_meiers_alpha_centauri), download (download as zip, mid right of this page), and unzip into your installation folder overwriting all duplicate files.
Some extra tools may be useful enough to be worth including, but I'm not certain which will have enough general use to qualify.