Both "Rapture: The Second Coming" and "Armageddon" are RPGs dealing with the end times, i.e. the Apocalypse.
"Rapture" approaches that topic more from the theological side with the characters mostly being members of religious organizations while "Armageddon" is somehow an independent extension of the WitchCraft RPG, mixing magic, mythologies and religions to an interesting blend. "Armageddon" is more action-orientated whereas "Rapture" focussed more on a sinister, pessimistic atmosphere.
I own both systems and I have run two adventures for "Rapture" quite successfully; in spite of the theological background it is not a sermon, it's a good game. As far as I know it is out ouf print; "Armageddon" too, but that one will be released again in November 2001.