The 6.3 version of OpenOSX Grass for Mac was available to download on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The actual developer of this free Mac application is OpenOSX. According to the results of the Google Safe Browsing check, the developer's site is safe. Despite this, we recommend checking the downloaded files with any free antivirus software. The program lies within Education Tools, more precisely Science.
From the developer:
GRASS GIS (Geographic Resources Analysis Support System) is a complete Geographical Information System (GIS) with raster, topological vector, image processing, and graphics production functionality. Grass is the open source alternative to ArcGIS with the spatial analysis module.
You may want to check out more software for Mac, such as GrassGames eBook Reader, GrassGames' Cribbage or LawnMowerKids, which might be related to OpenOSX Grass.