Terragen is a terrain generator; you can design and model digital landscapes that can appear startlingly realistic. The landscapes can feature water, clouds, rocks, grass and other types of plants and so on. This and other software like it are actually used in movies and TV. It may sound geeky and dull, but if you have ever created a "world", it's quite a thing to see and enjoy.
I first became aware of Terragen several years ago, with the original version of the software. It was surprisingly easy to use and actually rendered quite quickly even on the slower PCs back then. "Rendering" is the final step of the creation process, where the computer takes the scene you design and actually "draws" the final image.
|Terragen 4 main interface - click to enlarge|
The rendering process typically uses "ray tracing", which emulates the way real objects are affected by light, so the resulting images can appear to be very "real". Be aware that rendering can be slow for more complex scenes, and may take many minutes even on a fast PC as the ray tracing involved is quite demanding. If your video card has a modern GPU that will help a lot.
The current version of Terragen that is freely available is Terragen 4, and you can use if freely for non-commerical use, with some restrictions. These restrictions include the maximum size of the image (a not unreasonable 1200x900 pixels), and some limits on other settings like anti aliasing. Also, animation is disabled in the free version.
There are no watermarks in the rendered images, and so they are quite usable. You do not have to register or jump through any other hoops to download the software, which is available for Windows and Mac. There is certainly enough functionality in the free version to get a good feel for what the software can do and even to produce some good-looking images.
The newer version of this software is naturally more complex and flexible than the one I played with years ago (which is still available in dusty corners of the Internet - look for "Terragen v 0.9").
That said, Terragen 4 is not rocket science in it's basic operation, even though creating complex landscapes such as those shown here need some effort and practice. There are plenty of YouTube videos on different aspects of using Terragen, so help is just a click away.