The biggest challenges, technically, are 3D graphics and Networking. Network interoperability between Linux and Windows will rarely happen, because companies often use the proprietary Directplay library which cannot be ported over to Linux. We have created a multiplatform alternative, called Grapple, and we hope that over time, some Windows developers may pick this up to use in their titles, allowing cross platform multiplayer.
So I would not be surprised if the globbing libraries, for example, will do NFD-mangling in order to glob "correctly", so even programs ported from real Unix might end up getting pathnames subtly changed into NFD as part of some hot library-on-library action with UTF hackery inside.linus torvalds
Tcl tends to get ported to weird places like routers.larry wall
I view the JVM as just another architecture that Perl ought to be ported to. (That, and the Underwood typewriter...)larry wall