I'm going to perform an abstract necro of two previous topics:
http://www.hard-light.net/forums/index.php?topic=76632.msg1521781#msg1521781http://www.hard-light.net/forums/index.php?topic=76746.msg1524311#msg1524311...To discuss one which assumedly is of interest to more people. That is, of course, 3D modeling work.
The subject at hand is brought about by a recent class project for an engineering surveying course. During which, I found a remarkable new use for the Free!Ship software which I pointed out in its own thread some time ago:
http://www.hard-light.net/forums/index.php?topic=73575.msg1452274#msg1452274FreeShip has the immensely useful utility of importing curves as defined by a text file. Thus, in a previous use of the software as a real-world example, I was able to assemble a canoe hull design very rapidly from given coordinates in an existing Excel file. In a similar fashion for the surveying project in question, all of the elevation values of a 100 x 100 foot grid were given after the field work was done. I merely needed to re-arrange the order of some of the coordinates in the text file from the Excel file to be able to plot the terrain model:

Now, there was some additional work to perform in AC3D, as the model was mirrored on the wrong side, etc. But, the program's subdivision system retained all given elevations as closely as possible to those entered in the initial text file, thus rendering a very realistic terrain plot. Most other programs I know would not have achived those kind of results without much effort and hair pulling, if you will...
But, there is so much good stuff to find on Sourceforge besides the aforementioned software...
Continuing on with terrain modelers, check this one out:
http://sourceforge.net/projects/planetgenesis/It lacks documentation. It is entirely dependent on other software. It will not deliver exceptional first time results, and may need manipulation of the eported file to be of any use. But nevertheless, IT DELIVERS!

The above image is one which was created with some random variables thrown together. Although the vertical relief of the surface is really... non-expressive, the surface itself has the makings for rendering an absolutely terriffic ground texture. The program will also generate planets, which will be of interest to those wanting to render skyboxes.
I could go on, but the easiest and best thing to do now is simply post this link:
http://sourceforge.net/softwaremap/?&fq%5B%5D=trove%3A109And go from there. There's a lot of great projects on Sourceforge, and probably too many to try out. In any sense, whether it's free or not, discussion on software is welcome.
