emulator

n. imitator; rival

An emulator duplicates (provides an emulation of) the functions of one system with a different system, so that the second system behaves like (and appears to be) the first system. This focus on exact reproduction of external behavior is in contrast to simulation, which concerns an abstract model of the system being simulated, often considering internal state.
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Noun
1. someone who copies the words or behavior of another
(synonym) copycat, imitator, ape, aper
(hypernym) person, individual, someone, somebody, mortal, human, soul
(hyponym) epigone, epigon
(derivation) emulate

n. emulator, imitator

(n.)
One who emulates, or strives to equal or surpass.