Re-invent Your Desktop with Plasma!
There's so much more to say about Plasma and its technologies, but I'm out of space. The Resources for this article include many useful references to help make your desktop (or whatever your Plasma is running on) a better place.
Complete Qt documentation, with tutorials and examples is at doc.qt.nokia.com.
The full KDE API documentation is accessible at api.kde.org.
TechBase, a wiki for KDE developers can be found at techbase.kde.org.
Another great introductory tutorial is techbase.kde.org/index.php?title=Development/Tutorials/Plasma/GettingStarted. All other Plasma tutorials (including tutorials for non-C++ languages) are at techbase.kde.org/index.php?title=Development/Tutorials/Plasma.
The KDE examples module, a new KDE module released with KDE 4.4, contains example code, including (but not limited to) Plasma plugins. Your distribution should have packages available, but if not, you can browse the SVN repository via websvn.kde.org/trunk/KDE/kdeexamples, or you can download a tarball from ftp.kde.org/pub/kde/stable/latest/src.
The full source code for the applet described in this article is available at ftp.linuxjournal.com/pub/lj/listings/issue190/10638.tgz.
You can contact the Plasma developers and applet writers via the mailing list email@example.com, or by joining the #plasma channel on the Freenode IRC network. Don't hesitate to contact us if you need some help!
Riccardo Iaconelli has been a KDE developer since 2005. He is one of the core Plasma developers, and he is part of the team that gave birth to the project. Riccardo also is a member of the Oxygen team, the project that strives to bring beauty to KDE 4, working both on the code and the artwork. He currently is attending his last year of high school in Milano, Italy.