"Touched by an Alien" http://freedrama.net/aliens.html
On the surface the script is humorous. But it has added topics for discussion such as conquering other races and the prejudice against people who are different.
"Rock! Sword! Firecracker!" http://www.freedrama.net/firecracker.html
This script has a lot of flexibility for cast size and students can act out the Master's story. This can teach students to listen for directions from the Master and act out what is being said.
And here is one more script that is a simple physical comedy that can be fun to act out as well:
More Free Plays: