There's an open-source replacement engine for Keen 1-3, actually. It seems much progress has been made on something for 4-6, as well. I don't know if anyone's tried to port any of them to Android, but it sure seems feasible.
Keen 1-5 are, of course, legally obtained very cheaply through Steam.
Y'know, when I saw the news that Atari (nee Infogrames) was auctioning off some of its properties, it occurred to me that Keen might see the light of day again. Maybe if they strike a deal with Bethesda for something else?I hope we get Aliens Ate My Babysitter sometime.