Which game had two protagonists exploring parallel versions of a ruined city? [closed]

I'm trying to recall the name of a game I played from my father's Windows PC game collection sometime around 2007. Although my memory of it is a bit murky, I recall the protagonists were a man and a woman, who were exploring an abandoned, high-tech city. I also recall that for some reason, the two could only interact via some audio communicator- even when they were in the same area, they couldn't see each other, and the area was slightly different depending on which one I was playing. They didn't understand the mechanism behind this, at least at first, and the game hinted they were in parallel timelines or different eras. It was first-person, and had a heavy emphasis on environmental puzzles. I thought for some time it was related to the Myst series, but I've ruled out each of those games.