A Visual Guide To Alien Beings (Book, David W. Chace, 1996)
You can read it here. It's huge.
Unearthly Beasts and Other Strange People (Book, Jay Williams, 1979)
You can digitally borrow this book here.
Helious I & II (DOS, Sean Puckett/Albino Frog Software, 1993)
The bizarre formerly-shareware DOS game its creator claimed was so weird because it was made by aliens. The video below has the story. Play the games yourself in your browser here.