My 2 cents. It depends, what sense you put into portability. SqueakNOS can run on any intel-based architecture. But you don't have OS and need to implement all low-level stuff by yourself. No matter what software, I think you can claim that it is portable only to certain degree. To my opinion, it is better to have software which runs perfectly on some concrete platform, rather than have buggy/incomplete and with limited feature set (because of minimum common denominator) software which runs everywhere. Apple's success with IOS platform is a good showcase for that. An opposite example is web "platform". Despite the great progress in last decade, it is still far behind from desktop-based software in terms of responsiveness, speed and resource usage. -- Best regards, Igor Stasenko.