ComputerWorld has an interesting commentary from Nicholas Petreley. He looks at the development library that runs KDE, and also happens to be a dandy tool to develop software for nearly every popular platform. But with all this fuss being made about C# vs. Java and the competing frameworks, it's easy to forget that there are many other options for application development. My favorite is Qt, from Trolltech AS. The latest version of Qt, Version 3.0, is the foundation for the phenomenal K Desktop Environment (KDE). I'm crazy about KDE 3.0, so it should come as no surprise that I'm equally enamored with Qt.
Qt is a set of C++ libraries and visual development tools. It's available for Windows, Mac OS and just about every flavor of Unix-including Linux-and many handheld devices, such as the Sharp Zaurus. The Qt application programming interface (API) is virtually identical for all desktop platforms, so you can create a single source-code base and should be able to compile it without modification for all the supported operating systems.