When d20 Modern first came out, my brother was running a Ravenloft game, and I came home from college one weekend and ran a special session for his group. The players were hurled into an alternate universe, arriving in "Raven City" which converted the Ravenloft setting into a big city. It was very Shadowrun-esque, with a big megacorporation controlling Raven City, and a special paramilitary security force called M.I.S.T. that prevented people from moving through the toxic clouds that surrounded the city, isolating it from the rest of the world. It was a lot of fun.
Something like Forgotten Realms 2325 could be a lot of fun, and as some people suggested Dragonstar might be a good inspiration.