Platforming script = Environment System
Custom Item System is a general term so it's a "Script Key Term" while "Custom Inventory System" would be the "Type" that I am using already.
A system that makes some stuff more convenient or easy to use would depend on what it does. i.e. If it's a debugger, it's a Misc System. If it's a frame rate changer, it's a Misc Add-on. If it makes enemies stop using skills that inflict status effects if they are already incflicted (e.g. a better AI), it's an Enemy Add-on.
I think that I covered most of the possible key terms, but I'm not sure so I am asking. You'll have to help me edit the posts in scripts database later, SRK. Or we can do it now, come on IRC.