TerraVista for Mac

From Roman Schlegel:

TerraVista is a small application which displays the current day/night cycle of the earth using OpenGL. It uses textures made from satellite images for the day and the nightside to make it look realistic and the newest release also downloads real-time cloud cover images from the internet for an even more realistic experience.

The view location (i.e. the angle from which the earth is seen) can be customized either using a preferences dialog or by command-dragging the earth. The floating window which displays the earth can also be made translucent and the brightness of the nightside can be changed.