Alternative operating systems
A number of third party operating systems have been developed for the C64.
GEOS for the Commodore 64
As well as the original GEOS, two third-party GEOS-compatible operating systems have been written: Wheels and GEOS megapatch. Both of these require hardware upgrades to the original C64.
Several other operating systems are or have been available, including WiNGS OS, the Unix-like LUnix, operated from a command-line, and the embedded systems OS Contiki, with full GUI. Other less well known OSes include ACE, Asterix, DOS/65 and GeckOS.