Most dynamic languages can run on multiple platforms. IronPython and IronRuby are no exception. The dev teams are investing lots of resources in order to make this happen because of the importance of this feature to the community.
IronPython and IronRuby can be run on top of Mono, which enables you to run .Net applications on top of different platforms, including Linux, BSD, Mac and more.
There are some great posts that show you how to do that:
Enjoy the cross-platformability! :)