The original Quake 1, right in your browser!

To start, press any key. Arrow/WASD keys to move, Ctrl to shoot, space to jump, mouse click/drag to pan, Esc to pause.
Hold Tab to check monster killed/left and time taken. You can press the numbers 1-8 to swtich weapons if you have picked them up. If you die, press any key to continue.

On the menu, use arrow keys to move the cursor and Enter to select an option. You can change the controls in the options menu. Have fun!