Wine - Open Source Software for running Windows applications on other operating systems.
Altirra - Altirra is designed with emulation quality in mind, sometimes over speed and polish.
CodeWeavers CrossOver - Don't buy a Windows license, don't reboot and don't use a Virtual Machine. Try a free trial of CrossOver to run your Windows software on Mac, Linux and Chrome OS.
Steem Engine - Steem is an open source Atari STE emulator for Windows and Linux.
WineBottler - WineBottler is an App to manage and wrap your Windows apps into convenient OS X apps.
Hatari - Hatari is an Atari ST emulator for Linux and other systems that are supported by the SDL library.