Marble is a cross-platform virtual globe, an open source Google Earth-like tool with a host of interesting applications.

The program opens with a view of the Earth as a globe, and navigation is initially similar to Google's offering. You can left-click and drag to rotate the planet, while spinning the mouse wheel zooms you in and out. Cities are highlighted, and clicking one will give you more information about it (including a tab with the relevant Wikipedia page).

The standard satellite view only zooms in to world atlas level, but fortunately Marble has plenty of other options. Click OpenStreetMap in the left-hand Theme list and you'll be able to get right down to street level, with road numbers, street names and plenty of other details (parking, restaurants, theatres, hotels and more).

There are also tools to search for places, measure the distance between two points, or create routes to help you find your way from one point to another.

And if this isn't enough, then there are a host of bonus maps you can use. There are historical world maps from various dates, for instance. You can view maps showing the Earth at night, or highlighting temperature, or rainfall. Or you might venture a little further, with maps of the moon, Mars, Venus, Jupiter, Saturn and more (the Maps page will show you what's available).

Google Earth's search tool, Street View, its many photographs, and enormous amount of detail on just about everywhere mean it's still going to be the superior program for most people. But that's hardly a surprise, considering the money Google has poured into it. And it doesn't take away anything from Marble, which is a powerful, versatile and easy-to-use product, free software at its very best.