Good shout on OpenTTD, it's brilliant.
A Link To The Past / Super Metroid Crossover Randomizer - this is utterly brilliant, especially if you love LTTP / Super Metroid.
Basically, both the games are combined with locations that transport you between the two games (map rooms in SM, fortune teller caves in LTTP etc) The items for both games are in randomized locations across both games (so items for Zelda could be in Metroid and vice versa) so some serious exploration is required. There is logic built in to ensure that each seed is completable. It's amazing fun and well worth checking out.