I like wxWidgets; it is a nice way to write graphical user interfaces in C++ (though some people will say that writing graphical user interfaces in C++ is stupid, and that you should use C# instead, but I digress). In particular, wxAUI is a nice quick way to create interfaces with draggable / resizable / floatable / dockable / splittable panes / tabs and all that jazz, and wxScintilla/wxSTC is a nice wrapper around Scintilla to give you the basis for a very nice code editor control. One problem with wxAUI is that most people use the default theme, so the default theme begins to look common once you've seen a few wxAUI-based applications. The default theme is also starting to look a little bit dated and old. Conveniently, wxAUI was structured to have pluggable art providers, meaning that it really isn't too hard to write a completely different theme for it. I've taken advantage of this feature of wxAUI to give a Visual Studio 2010 theme to applications written with wxAUI. The end result looks like the following:

For reference, the same application using the default wxAUI theme looks like:

For reference, Visual Studio 2010 looks like:

Most of the process of implementing this is obvious: take the code for the default art providers, rip out most of their innards, and replace them with new drawing code. There are however a few difficult steps:

PS. Yes, my current project is a Lua IDE / debugger.