This is a simple script I made for my server, but due to slightly popular demand, I am uploading it here.

README.txt:
"Place the above 2 folders in garrysmod/garrysmod on your server.

sv_maxnoobs <number>
Sets the maximum amount of players allowed onto your server who aren't in coolplayers.txt

sv_addcoolsteam "<steamid>"
Adds the desired Steam ID to coolplayers.txt
*Note: needs quotes around the steam, and does not check the entered string, so you can write anything really.


This can be useful for many things:
Set maxnoobs to 0 and add all your friends steam IDs to coolplayers.txt in order to only allow your friends on
Set it to a low number so your server doesn't fill up with random players
Set it to any number greater or equal to your server total in order to allow random people to fill up your server



MORE NOTES:
You can always manually edit coolplayers.txt, it's located in data/coolplayers.txt
The concommands are serverside only"