KEGS-Apple IIgs emulator for Mac OS X, Win32, Linux, and Unix/X11

KEGS emulates an Apple IIgs accurately at between 8MHz and 120MHz on pretty much any Unix/Linux computer, Win32, or Mac OS X.

CREDIT

Qemu

From the Website:

QEMU is a generic and open source processor emulator which achieves a good emulation speed by using dynamic translation.

QEMU has two operating modes:

• Full system emulation. In this mode, QEMU emulates a full system (for example a PC), including a processor and various peripherials. It can be used to launch different Operating Systems without rebooting the PC or to debug system code.
• User mode emulation (Linux host only). In this mode, QEMU can launch Linux processes compiled for one CPU on another CPU.

An optional proprietary QEMU Accelerator Module is available to optimize the case where a PC is emulated on a PC. This module enables QEMU to run most of the target application code directly on the host processor to achieve near native performance.

The supported host and target CPUs are listed in the status page. For full system emulation, the supported Operating Systems are listed here.

QEMU for Mac OS X

SIMH

From Wikipedia :

SIMH is a highly portable, multi-system emulator which runs on Windows, Linux, Mac OS X, FreeBSD, OpenBSD, NetBSD, OpenVMS, and other operating systems. It is maintained by Bob Supnik, a former DEC engineer & DEC vice president and has been in development in one form or another since the 1960s.

Emulated hardware List

Installing OpenBSD/vax port on simh-vax

The Hercules System/370, ESA/390, and z/Architecture Emulator

From the Website:

Hercules is an open source software implementation of the mainframe System/370 and ESA/390 architectures, in addition to the new 64-bit z/Architecture. Hercules runs under Linux, Windows (98, NT, 2000, and XP), and Mac OS X (10.3 and later).

Hercules is OSI Certified Open Source Software licensed under the terms of the Q Public Licence.