GEOS closely resembles early versions of the classic Mac OS and includes a graphical word processor (geoWrite) and paint program (geoPaint).

At its peak, GEOS was the third-most-popular microcomputer operating system in the world in terms of units shipped, trailing only MS-DOS and Mac OS (besides the original Commodore 64's KERNAL).

Written by a group of programmers at Berkeley Softworks, the GEOS Design Team:[4] Jim DeFrisco, Dave Durran, Michael Farr, Doug Fults, Chris Hawley, Clayton Jung, and Tony Requist, led by Dougherty, who cut their teeth on limited-resource video game machines such as the Atari 2600, GEOS was revered[citation needed] for what it could accomplish on machines with 64–128 kB of RAM memory and 1–2 MHz of 8-bit processing power.

The C64 version of GEOS incorporates a built-in fast loader, called diskTurbo, that significantly increases the speed of drive access on the slow 1541.

On August 19, 2016, Michael Steil posted in his blog[9] that the source code for GEOS 2.0 for Commodore C64 had been fully reverse-engineered and suitable for the cc65 compiler suite.

The magazine approved of geoWrite ("you could easily be fooled into thinking that you were using MacWrite"), geoPaint, fastloader, and documentation, and concluded that "GEOS has given the C64 a complete face-lift and a new lease on life".