XWinSpector is an application that allows you to view the list of windows with their children like Spy++ does (in a tree view).
Using this application you can discover hidden features of other software!
It allows to show hidden windows, it allows to enable disabled windows etc.
Example of XWinSpector usage on windows run dialog (it discovers hidden "Run in separate memory space" checkbox): http://www.youtube.com/watch?v=Zg8dW5FBbh8

Скачать XWinSpector бесплатно на странице загрузки.