Do you want to "try before you buy"? Or don't think you would need the full version of Distant Suns? Then please download the Distant Suns 4 "special edition". This is not a crippled demo, but the original commercial version minus the larger specialty files that would have made it impossible to download.
However, if you want the latest and greatest, then you might want to consider purchasing the just released, Distant Suns 6.0. Version 5.3 is faster than DS4, sports all sorts of new features, has much better planetary rendering, telescope control, over 16 million stars, along with additional databases, video files and images.
(if you are looking for the SETI@Home version, click here)
Having DLL problems with this download? A few users have indicated that they get a warning that either "tbpro4w.dll"or "mfc250.dll" is missing when trying to run the program. Technically these file are not needed, but some configurations of Windows seems to think that they are. If you are having this problem, download the missing files you need here, unzip them, and place into your windows/system directory. You should see other "tbpro" files there if you want to verify that this is the proper location.