FreeOrion is a bit too heavy for newcomers, but for fans of the original certainly a great open source alternative. P>
The CHIP editors say: p>
Conquer entire galaxies in the free space game FreeOrion. P> FreeOrion Free Orion is an open-source clone of the turn-based strategy game Master of Orion. Like in the prototype you start on a small planet and finally have to conquer an entire galaxy.
In all likelihood, you will encounter foreign peoples with whom you can either wage peaceful trade or destructive wars.
Research and production at FreeOrion determine the well-being and woe of your people. A helpful online wiki helps you get started.