The console versions start with one member of your crew ending up on an island whereas in the DS version, you start in a crate.
The console versions are developed by The Sims Division whereas the DS version is developed by Full Fat.
The Sims 2: Castaway is a console/handheld only game. There is no PC expansion for Castaway although The Sims Castaway Stories is a standalone game and as stated above, it is unrelated to The Sims 2 although they do use the same game engine.
In Castaway Stories, Sims age and can have children, whereas in the console versions they stay adults forever.
In Castaway Stories, there is a limited variety of supplies, whereas the console version contains a larger variety of available supplies.
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