Galaxy '93

CHEAT MODE:
During play press '`' (the key right below the 'ESC' key). Quickly enter "23863" on the numeric keypad. The high score should change to all 7's. This gives you infinite lives and you can use the following keys:

SPACE - Kill yourself.
D - Advance one level.
N - Advance to the next bonus stage.
A - Displays a section of the code in HEX.

(Source: Aminet CheatsCodes)