Those are not entirely correct.

Shift + O spawns a helicopter. You can't control it, it's just decorative. Spawning more than two or three helicopters crashes the game.

Shift + A spawns a Wild Cat nearby who will try to attack you.

Shift + I spawns Gordansky. She will follow you and automatically attack any foes nearby. If you spawn multiple instances of her, they will start getting in each other's way, causing friendly damage and fighting for real.

I disassembled the game years ago - there are interesting things and leftover debug functions not mentioned in that page, for example (only when the cheat mode is enabled):
Shift + M spawns a mine.
Shift + F3 performs a quicksave (which doesn't work properly, it was probably disabled during development, long before completion), F3 tries to load it and crashes.
S tries to save a screenshot into C:\tmp\ . Badly implemented and very annoying if your control scheme is WASD...

hey thanx, worked great!
now with the 1080 resolution & with working cheats this already awesome game got so much better!
such an underrated gem this game is.

Can you spawn any npcs other than Gordansky and the wildcat?

Yes, if you do some hex editing on fallen.exe .

The byte at 0x014B63 defines the class of the badguy to be spawned through Shift + A.
The byte at 0x14C16 defines the same for Shift + I.

These values correspond to the following:
0 - Darci (if she knocks you down, she will arrest you and mission will fail)
1 - Roper (you can't hit him)
2 - Cop (you can't hit him, he will probably try to arrest you as well)
3 - Male civilian
4/5/6 - Wildcat
7 - Hooker
8 - Female civilian
9 - Gordansky
10 - Worker wearing overalls
11 - Old man wearing black leather jacket
12/13/14 - Man In Black (dangerous...)

Thanks, but I can't find the values using Hxd. I'm using the 1080p exe and want to swap Gordansky to a Cop

Take a look at the image I'm attaching - the selected byte is the one you should be changing. If you change it to 02, Shift + I will spawn a cop instead of Gordansky.

Thanks for the help.Works perfect, The cop even helps in fights just like Gordansky. When possible he will arrest enemies as well.

So cheats that can make the game much easier are available? Hmm, I'm not sure I could play it vanilla as I'm spoiled by new "save-anywhere" games, but having some significant help intrigues me. :) Ha ha, as someone who's quite pro-Second Amendment this makes me facepalm, but I'm still quite glad there's an invincibility cheat. ;)

A true invincibility cheat doesn't exist in this game. The closest you can get is F12 which puts your health to 10000 instead of the usual 200 (without rescaling the health bar, which makes it look like you're invincible), but you are still vulnerable to damage.