It basically shows up a simple FrameWindow with a listbox showing all members of your current TS3 channel, while someone is talking, his name is highlighted.
What's special about it, is that this information is shown within any D3D8, D3D9 and D3D10 game.
I chose the CEGUI to do that, as I noticed, that I put too much time in developing my own "custom" controls for all those DirectX versions around there. As I want to improve the overlay a little bit more (more controls, probably multiple channels at a time, drag&drop or something), CEGUI seemed the right thing to use. A step I didn't regret so far
You can find the overlay under http://ts3overlay.r-dev.de
I'm glad you like CEGUI so far, and hope you continue to like it 