Steem Engine is described as 'Steem is an open source Atari STE emulator for Windows and Linux. It runs almost every ST program ever made without any problems. Steem is designed to be easy to use and has many unique features'. There are more than 10 alternatives to Steem Engine for a variety of platforms, including Windows, Mac, Linux, BSD and Self-Hosted solutions. The best alternative is Stella, which is both free and Open Source. Other great apps like Steem Engine are Z26 (Free, Open Source), Hataroid (Free, Open Source), Javatari (Free, Open Source) and ProSystem (Free, Open Source).
Stella is a multi-platform Atari 2600 VCS emulator released under the GNU General Public License (GPL). Stella was originally developed for Linux by Bradford W. Mott, and is currently maintained by Stephen Anthony.
jGameBase is a fully-featured retro-gaming emulator frontend and game database utility. It is a sister application to the Windows program GameBase (without "j"), the official frontend for the GB64 Collection.
PCE is a collection of microcomputer emulators. At the moment it contains three emulators: PCE/atarist is an Atari ST emulator. It emulates the various ST and Mega ST models. PCE/ibmpc is an IBM PC 5150 emulator. It emulates an IBM PC 5150 or an IBM PC/XT 5160.
This is the the Macintosh OSX Port of David Firth's Fantastic Atari 800 Emulator. Ported is the SDL version of the Atrari800 emulator to Mac OSX, and added a full native Cocoa interface, including Preferences, Menus, File Associations, Help and more.