What is it?
Xearth sets the X root window to an image of the Earth, as seen from your favorite vantage point in space, correctly shaded for the current position of the Sun. By default, xearth updates the displayed image every five minutes. The time between updates can be changed using either X resource or a command-line option. Xearth can also be configured to either create and render into its own top-level X window or render directly into PPM or GIF files; see the man page for details.
Version 1.1 of xearth includes several new features:
Information about previous versions can be found in the HISTORY file that ships with the version 1.1 sources.
Where to get it?
A gzip-ed tar file containing sources for the latest-and-greatest version of xearth is available as xearth-1.1.tar.gz (154 kbytes).
Several people have ported xearth to other platforms. These links are provided for reference purposes only: I had nothing to do with these ports, so if you've got questions about them, I probably can't help you.