EmuTOS is a single-user single-tasking operating system for 32-bit Atari computer emulators, like ARAnyM, STonX or Hatari . It is designed as a replacement ROM for the TOS images you usually need today for using emulators, and it also runs on some real hardware, like the Atari Mega STe or the FireBee. Everything is Free so maybe EmuTOS will run on totally new machines in the future.
Since EmuTOS just implements the TOS's functionality, you might want to use MiNT on it in order to run more modern software. EmuTOS is not an alternative to MiNT. But EmuTOS is the only Free base OS to boot MiNT.
You will find more information about EmuTOS on the SourceForge project page at:
The EmuTOS development team