I'm searching for a noun (a single word if possible) or phrase that conveys that one thing functions the same as another externally, even though the internals may differ.
Nouns such as copy, a clone, duplicate, or substitute capture only part of my meaning. Additionally, these words often have a negative connotation; they imply that the thing is derived and possibly inferior. But I don't want to imply that the other thing is derived or merely copied.
What might be some good words or phrases that give a positive connotation, perhaps giving a sense of rethinking, "re-invention", or possibly renewal? I don't need the word to necessarily signify that the new thing is alive, but I want to avoid implying that it is 'lesser'.
Here is an example sentence:
LEG, a recent upstart in the electronics industry, has released the Tintium line of microprocessors, a [?] of Intel's Pentium line of processors. It behaves identically, but since it uses tin-arsenide for its substrate, the chips offer better reliability, especially for interstellar applications. The chip design is open source; several industry experts claim its internals are simpler and more efficient than the Pentium.
After losing his biological leg, Alan sought the services of Biocraft LLC, who custom designed and attached a [?] of his original limb. The company says it will outlast the natural leg.