Is there chess software to play against that rates your skill through actual games? Is there chess software out there that will try and rate your play? I vaguely recall an old Chessmaster software that did something similar, though by having you play through puzzles. I was looking for an actual engine to face you and gauge an estimated Elo rating somehow.
I realize what I'm about to suggest isn't exactly what you have in mind, but still, it is technically software, and it rates your skill through actual games: play games online against other people, e.g. at FICS, Playchess, ICC or chess.com.

Instead of using some software that would have you play games against an engine (perhaps with various "levels" that are supposed to reflect various Elo levels), and then has some algorithm or other that tries to convert your results against it into your own estimated real-world rating, my suggestion cuts out the middleman and throws you right into a real-world pool. This way seems more efficient if nothing else (and probably more fun).

Now any rating you get at one of the sites I mentioned will be on a somewhat different scale than that for, say, actual FIDE ratings, and they will differ from site to site as well. But you will usually have some way to translate your rating there into a percentile (within that site's playing pool), and that would give you better information about your playing strength than any purely algorithmic guess about it will.