GEOS

Parts of this article have been copied from Wikipedia's page about GEOS.

GEOS is an acronym that stands for Graphic Environment Operating System. It was originally developed by Berkeley Softworks and the first version was released for the C64 in 1986.

Versions (contains info from C64 wiki) :

GEOS Version	Release year	Notes
1.0	1985	Beta version for developers
1.1	1985	Beta version for developers
1.2	Jan. 1986	First version available for customers
1.3	June 1986	First version for other languages
1.5	1987/88	GEOS version that got bundled with the C64C
2.0	June 1988	GEOS 2.0 is presented in the CES in Las Vegas
2.5	1993	German publisher Mark & Technik developed this version in collaboration with “GUC - GEOS User Club”
3.0	?	MegaPatch3 is developed as third-party project.
GDOS64	?	Third party project,