[jinjin2]

I guess there are two ways to define cross-platform. The obvious one is the software being available for more than one platform, but since that could really be accomplished with two separate implementations, there is also the more generic definition as a piece if software that is build in such a portable way that it can easily be ported to any platform.

Since Realm is available for iOS, Android and Linus from one code base(and open source, so you could port it to other platforms) I would definitely term it as being cross-platform.