Atari
Atari ST emulation on Amiga is very easy because the two machine share the same model of processor (68000) and more or less feature the same hardware characteristics.
In the past there were produced various software based Atari emulators for the Amiga such as Amtari, or Medusa emulator.
Modern Amiga-like platforms such as Pegasos equipped with MorphOS operating system, emulates Atari ST and Atari STE platforms with Hatari open source emulator released under GPL.
Read more about this topic: Emulation On The Amiga