gr2 is: Gr2 extension is associated with Granny 3D File. You have chance to open GR2 files with Granny 3d software on your computer.
GR2 extension stands for 3d drawings which created in Granny 3D software. GRN and GR2 files can be used with various 3D softwares. If you need to convert grn files to gr2, you may use grn2gr2 program. The web page of the software includes different kind of tools.
To get detailed information about the software, please take a look to following web page.
Gr2 File format viewers or openers
Gr2 File related links.