Zaxxon

Invincibility:
Repeatedly type RED at the title screen until the word "Red" appears.

Cheat mode:
Load or reset the game, then execute the following BASIC command before running or restarting the program.
POKE 34488,173

Set number of lives:
Load or reset the game, then execute the following BASIC command before running or restarting the program.
Note: X represents the desired number of lives.
POKE 11353,X