The Atari ST is a line of home computers from Atari Corporation and the successor to the Atari 8-bit family. The first ST model, the 520ST, was released in June 1985. "ST" officially stands for "Sixteen/Thirty-two", which referred to the Motorola 68000's 16-bit external bus and 32-bit internals. The Atari ST is the first personal computer to come with a bit-mapped color GUI, using a version of Digital Research's GEM released in February 1985. The 1040ST, released in 1986, is the first personal computer to ship with a megabyte of RAM in the base configuration and also the first with a cost-per-kilobyte of less than USD$1.
The Atari ST is part of the 16/32 bit generation of home computers, based on the Motorola 68000 CPU, typically with 512 KB or more of RAM, a graphical user interface, and 3½"floppy disks as storage. The ST was primarily a competitor to the Macintosh, Amiga, and, in certain markets, the Acorn Archimedes. Whereas the Amiga has custom graphics processors and sample-based synthesis audio, the ST has a basic frame buffer and a 3 voice synthesizer chip but with a slightly faster CPU and a high-resolution monochrome display mode ideal for business and CAD. Its simple design allowed the ST to precede the Commodore Amiga's commercial release by almost two months.
Hatari is an Atari ST/STE/TT/Falcon emulator for GNU/Linux, BSD, Mac OS X, Windows and other systems which are supported by the SDL library. Hatari supports the emulation of most of the ST and STE hardware, including some special tricks like raster interrupts, border effects and PSG sample sound. A joystick can be emulated with the cursor keys or with a real PC joystick. Hatari also features the possibility to "mount" a directory of the host system as a ST drive, or to use images from an original Atari's hard disk. Hatari is also able to emulate the additional hardware of the TT or Falcon machines, like the Videl video chip or the DSP 56001. However, note that TT and Falcon support are currently still in development and experimental. You can download it from Hatari homepage.
Another great Atari ST emulator is NoSTalgia. You can find more specs and download at NoSTalgia homepage.
ARAnyM is a software virtual machine (similar to VirtualBox or Bochs) designed and developed for running 32-bit Atari ST/TT/Falcon operating systems (TOS, FreeMiNT, MagiC and Linux-m68k) and TOS/GEM applications on any kind of hardware. Download the latest version from ARAnyM Sourceforge page.