From publisher blurb:
Now you can play Alien and Robot Characters!
Alien Class Design: A space opera setting usually has numerous types of alien races - but statting out hundreds of different races can be a huge problem. Instead of choosing from a staggering amount of predetermined races, players can use this system to develop their own PC alien and creatively fill in the gaps.
Robot Class Design: Sometimes robots become sentient - it’s a staple of many sci-fi and pulp stories. Even some “stock” robots in popular fiction seem to be “more” than they were intended to be. Presented here are rule suggestions for those players who wish to play a robot that is “more” than the stock options presented in the X-Plorers core rules.