The newest version of Spim is called QtSpim, and unlike all of the other version, it runs on Microsoft Windows, Mac OS X, and Linux—the same source code and the same user interface on all three platforms! QtSpim is the version of Spim that currently being actively maintaned. The other versions are still available, but are no longer maintained or updated.
A compiled, immediately installable version of QtSpim is available for Microsoft Windows, Mac OS X, and Linux can be downloaded from:https://sourceforge.net/projects/spimsimulator/files/. Full source code is also available (to compile QtSpim, you need the Qt framework, a very nice cross-platform UI framework that can be downloaded from http://qt-project.org/downloads).