Start the game with the hl.exe -dev -console -game action command
line. This enables the console window. You can enter the original
Half-Life missions with Action Half-Life's weapons and models. 
The scientists, aliens, and Barneys are the same and are fun to 
kill. When you enter the single player mission, display the console
window and type sv_cheats 1 to enable cheat mode. Then, type /god 
for God mode, /impulse 101 for all weapons, /noclip to fly around 
through everything, and /notarget for everything to ignore you. 
Note: The game will eventually glitch.