I just became aware of NASA’s World Wind software. World Wind is, in many respects, similar to Google Earth, the difference between the two being more in philosophy, than anything else.
World Wind is totally OpenSource, and has a focus on visualisation of scientfic data.
World Wind includes high-resolution imagery of the Moon as well.
The imagery of the Earth, called Blue Marble, is breathtaking, it makes Google Earth look “flat” from the unzoomed perspective.
Google Earth on the other hand, has much more detail, and is better at covering the world with high-resolution pictures. This is mainly due to the fact that Google Earth uses commercial images from KeyHole.
If you absolutely have to compare the two, I think that Google Earth has a more intutive interface, is much faster- at least on my hardware, and with high resolution satelitte images covering large areas of the world, for Denmark this even includes labeled roads. So all in all, Google Earth is currently the most useful of the two, especially if you’re an “ordinary user” living outside the US.
That being said, both World Wind and Google Earth are truely fantastic applications, and as the World Wind FAQ suggests: use them both. I do however hope that World Wind, with it’s OpenSource model, will create a vibrant community, that will help make it more useful for international users.
It will be really interesting to see how these applications evolve.