Google's Picasa software is a powerful tool for managing your photo collection. It provides a simple interface for organizing your pictures, as well as some easy-to-use, yet powerful image manipulation tools. However, until recently the Windows version of Picasa has had some features that put it above the Linux version; some of these features, like Picasa Web Album integration, are at the core of the program, without which Picasa isn't very useful. With its newest release, the Linux version is being brought up to par with its Windows counterpart.
While it may not let you go where no man has gone before, Celestia is an amazing desktop application that lets you go anywhere in the known Universe.You can view any object in the Solar System, travel to distant stars, and even leave the Galaxy, traveling faster than the speed of light, viewing high-res images of objects millions of miles away.