noun.
One who or that which differentiates: as, the radicals of written Chinese serve as differentiators of the sense, while the phonetics play the same part as regards sound.
the GNU version of the Collaborative International Dictionary of English
noun.
Anything that differentiates, or causes differentiation (in any sense)
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
a person who (or that which) differentiates
Word Usage
"Their main differentiator is that it’s a classless, and claims to be more narrative and share interpretive power with characters (implied: at least more than D&D)."