as close to that as i have ever seen is:
Cursor Castbar
Originally a really neat idea for a castbar, it, sadly, has not been updated in a while, and i have not tested it since wow 3.1.
Don't be fooled by the name, it can be placed anywhere on the screen via the options, however, it IS a full circle, not a half circle that you are looking for.
Who knows, if you have add on experience, maybe you could mod it to be a half circle?
Hope this helped!