A full-featured anti-aliased highly-customizable analog clock for your for your home screen.

Comes with an editor to be run on your PC, called REdit (surprisingly a shorthand for Retro Edit), to assemble custom clock files and edit existing ones (see this short tutorial).
It also contains a sample clock named Modern, directly taken from Vista's sidebar.

Retro uses multiple PNG images with transparency for its compositing, placing them in up to 30 layers. This makes possible a wide range of effects, including superficial glass translucency, transparent clocks without background, chronograph-style clocks, and so on...