Diadem is a rewrite of something I did when I was working on Picasa. It’s a library for displaying and managing dialog windows, using the same code and resource files on Windows and Mac OS X, while also keeping a native appearance and layout on both platforms. Many of the windows in Picasa use it, including the Preferences window.
I rewrote the library as Diadem for two main reasons. First, the original version was too closely tied with Picasa, so it could not be packaged as a separate library. Second, I came to regret some of the design decisions I had made, and changing them would have been too disruptive to Picasa.
As a rewrite, Diadem only retains some of the most basic layout code from its predecessor. Beyond that, the similarities are pretty much only conceptual. The Mac and Windows parts have to be almost totally rewritten. The Mac version is functional, with some controls (most notably tabs) remaining to be implemented. On Windows, the cross-platform and XML parsing tests are working, while the native control implementations are still in progress. Additionally, there is a wrapper for using Diadem in Python.
For the moment, Diadem is not being used in any application, but it has been an interesting project to work on, giving me opportunities to learn more about Windows, Python, and good old API design.