ST Mint is a FreeMiNT distribution which provides an opensource Unix environment for the 16/32 bits Atari line of computers. The target platform are Atari ST(E), TT, and Mist FGPA board with at least 4 MB of RAM, 128MB SD Card drive, ST High Resolution.
St Mint is distributed in the form of a ready to boot disk image, to use for instance with Lotharek's UltraSatan drive
Download: ACSI disk image
After inserting the media in your Ultrasatan device, your ST should boot into ST Mint. After booting a 4MB machine, you should have around 1MB of RAM free for applications.
After a rather slow boot sequence, you should land on the desktop. Click on COMMAND.TOS, and 2048.APP and notice the two apps running simultaneously. Such a thing is not possible using the standard Atari TOS.
Click on the Desk menu list =⇒ TosWin2 =⇒ File =⇒ Start shell and enjoy /bin/mksh, a Korn shell clone. Note that due to the very limited hardware of the ST compared to current standards, you can at most only run simple Unix command line tools.
Use the downloaded .img file as an emulated ACSI device, and just boot. If you use the Hatari emulator, it would be:
hatari --acsi st_mint-1.3.img