EmuTOS is partially derived from Digital Research's original GEMDOS 1.1 operating system and GEM GUI. EmuTOS is basically made up of seven parts:
GEMDOS was first used in Apple's Lisa computer, and later, as home computers came up, in Atari ST series. In both GEMDOS were the base for Digital Research's GEM graphical user interface, which became very popular with the introduction of the Atari ST.
In 1999 Caldera bought all the GEM and GEMDOS stuff from DRI and thought of using it as a base for some thinclients. But this never happened and they decided to release GEMDOS together with GEM under the GPL (GNU General Public License).
In spring of 2001 we began to work on these old sources and had some good progress till today.
The BIOS and XBIOS code is our own development. It is really written from scratch and implements nearly all of the TOS 1.0 BIOS functionality, and a bit more, like e.g. hard disk access and STe sampled sound. A few things like printing, midi and serial stuff is missing for now, but may be implemented in the future.
The GEMDOS part is based on Digital Research's GEMDOS sources, which were made available under GPL license in 1999 by Caldera. Also all of the graphical parts, the VDI, AES and desktop, which are now nearly completely implemented. Though, many parts of these subsystems have been changed or rewritten to be more compatible and conforming with modern TOS developments.
Of course, being a single-user and single-tasking OS, EmuTOS can not compete with other modern operating systems that are available today. In the TOS world, all of GEMDOS has been replaced by a superior operating system called FreeMiNT (MiNT Is Now TOS). This is widely used in the Atari ST and TT series computers today. FreeMiNT is is more POSIX-like and provides most modern concepts, like a multi-user environment, symmetric multitasking, memory protection and so on.
But since EmuTOS provides the same functionality as the original TOS and the code is lean enough to fit within less than 256 KB ROM, it is a perfect replacement for the original TOS. So when talking about EmuTOS, maybe rather think about a cool firmware replacement for TOS compatible machines instead of a full-blown operating system.