I am having difficulty understanding the difference. I know that Carbon is something that is updated from Classic format to OS X, and Cocoa is OS X only. Java is supposed to run without recompile on all platforms with a Java Virtual Machine. (I.E. OS X, Mac OS Whatever, Windoze, Solaris) What I really need to know is what the .app suffix is intended for. the OS X developer tools that develop for Java compile a .app thing. I can\'t open it in OS 9, and I want to know if there is a way that this is possible. Is .app ever going to be added to a carbonized application, or is that just for Cocoa and (a mulitated, non-universal version of) Java?