Prey was released back in 2006 by 3D Realms. It had a colourful development history that spanned many years. It was made on the Id Tech 4 engine. One of the benefits the engine had was it allowed you to code in bots to play multiplayer with. Neither Doom 3 nor Quake 4 had this at launch. But for some reason Prey 2006 did.

Spawning bots is very easy to do but requires specific steps. Which are outlined bellow.

Step 1. Open the console by pressing Ctrl+Alt+ ~ (the key above the tab button right next to 1.)
Step 2. Type into the console "net_allowCheats 1 3"
Step 3. Go to multiplayer, select the middle tab "Create Server" and under "Server Type" toggle the word "internet" so it says "LAN" instead.
Step 4. Press create
Step 5. When in the server. Type in spawnArtificialPlayer

And that's it. By default you can only spawn a maximum of 3 bots unless you create a dedicated server. At which point you can spawn a lot of bots.