Terragen is a photorealistic landscape generator that is available for free for non-commercial use on both Windows and Mac (OS 9 and X) platforms.
The wide array of options and variables lets even the most amateur graphic artist create and render photorealistic landscapes. The whole process is as complex or simple as you want it to be. I personally like the program because by tweaking the variables, you could create a very realistic Mars or other planetary landscape. You can even use Terragen to create planet views from space. The program is so flexible and versatile, the possibilities are endless.
Tweak elevations, atmosphere, water levels, cloud cover, and a myriad of other options. The customization possibilities are endless.
While I normally focus on astronomy and current events, I believe this is a great addition to any armchair astronomer's arsenal of software, because let's face it, sometimes we just want to have fun and be creative.
Download Terragen for free at: