Perk system

PerkBox script is good.
Endless config, allows you to add as many perks as you want!
All perks save, friendly saving using the file system, you can easily delete files in data/perks.
Categories for all the perks.
Lightweight, will use little to none of your precious server resources.
Works as a tier system, you have to buy the worst, to work your way up to the best perks.
Very simple, spawn it in the spawnbox menu, save it with the persistent sandbox option, requires no extra addons.

I'm using this one too, you should use it.