NASA's got a whole section of Open Source Software at software.nasa.gov. This is an extensive catalog of software used by NASA at their various space and research centers. If you download from the NASA catalog, you've got to register and fill out a Software Usage Agreement form so that you can get a SUA.
Some of the software can be accessed via NASA's github account. You wont need to fill out a form for these programs. And, the selection is a limited in comparison to the actual NASA catalog.