This is the Crystal KDE Windowdecoration Theme. The theme is pretty simple and clean, but has very nice pseudo transparency within the border and the title bar. You can choose of other image effects too.
It is based on the KDE-WM "Example", which can be found here:
And it is modelled on the crystal fvwm2 style. Check it out:
Check out crystal at kde-look.org:
I hope, you like it.
- Sascha Hlusiak