Kkrieger is a portable first-person shooter in a single 95KB executable.
The program was written in 2004, and despite its tiny size, it looks and feels much like similar games of the day. You must run around a maze of corridors to an atmospheric soundtrack, picking up guns, ammo, health packs and more, while shooting assorted monsters before they get too close.
Controls are mostly keyboard-based, and also much the same as other programs: press W/ A/ S/ D to move around, space to jump, 1-5 to switch weapons, left mouse button to shoot, and Esc to pause or close a game.
PLEASE NOTE: Kkrieger doesn't run smoothly with modern Windows and PCs, and there's a good chance it won't launch at all on the default settings.
To run the program successfully, right-click pno0001.exe, select Troubleshoot Compatibility > Try Recommended Settings.
Alternatively, create a shortcut for the program, right-click it and select Properties > Compatibility. At a minimum, check "Run this program in compatibility mode for" and select "Windows XP (Service Pack 3)".
BEWARE: kkrieger needs to take full control of your hardware to run successfully, and this means running full-screen and grabbing your mouse. That's not an issue while you're playing, but if you Alt+Tab away, you might find you can't move the mouse or Alt+Tab back. To avoid problems, close kkrieger properly via the Esc menu rather than switch away, and ideally save any current work before you play the game.