James Alan Gardner's "The Ray-Gun: A Love Story" (novelette, mysterious gadget, free)

Easy read, but best of this class I've seen so far are superlative: Henry Kuttner/C L Moore's "The Twonky" & "Mimsy were the Borogoves" (download).

Story summary.

Circumstances ensure teenagers Jack & Kirsten get involved with a mysterious gadget of alien origin that ended up somewhere on earth. This gadget is the "ray-gun" - but it's much more besides being a weapon. Jack will pick it up, though the gadget will affect the lives of both Jack & Kirsten - entangling them romantically as they grow up. Besides having a mysterious purpose of its own.

Collected in.

1. Gardner Dozois (Ed)'s "The Year's Best Science Fiction: Twenty-Sixth Annual Collection" (2009).
2. Rich Horton (Ed)'s "Science Fiction: The Best of the Year, 2009 Edition".
   

Fact sheet.

First published: Asimov's, February 2008.
Rating: B.
Download full text from publisher's or author's site.
Among the preliminary & final Nebula Award 2008 nominees in novelette category.
Nominated for Hugo Award 2009 in novelette category.