GRASS is a Geographic Information System that was originally developed by the US Army's Engineering Corps and was then open sourced and is now being actively developed by Universities and volunter programmers and users from around the world.
Here is the blurb from the debian package info

Geographic Resources Analysis Support System, commonly referred to as
GRASS, is a Geographic Information System (GIS) used for data
management, image processing, graphics production, spatial modeling,
and visualization of many types of data. Originally written by the
U.S. Army Construction Engineering Research Laboratories (USA-CERL)
branch of the US Army Corp of Engineers as a tool for land management
and environmental planning by the military, GRASS has evolved into a
powerful utility with a wide range of applications in many different
areas of scientific research. GRASS is currently used in academic and
commercial settings around the world, as well as many governmental
agencies including NASA, NOAA, USDA, the National Park Service, the
U.S. Census Bureau, USGS, and many environmental consulting companies.