PowerST is an Atari ST emulator that is based on NoSTalgia, but makes use of the Asgard 68000 assembly engine, making it capable of running the GEM Desktop at full speed on any Power Macintosh. It also supports the following: Atari TOS 1.0,...

SIDPLAY is a music player software. that emulates the Sound Interface Device chip (MOS 6581, known as SID) and the Micro Processor Unit (MOS 6510) of the Commodore 64 on the Mac OS.  SIDPLAY is not related to the music...

SPIM/SAL emulates the MIPS R2000/R3000 RISC computers. 

MacMESS is a port of MESS (Multi Emulator Super System) to the Macintosh. It has a very long list of supported computers and game consoles, including Amstrad, Apple, Atari, Commodore, IBM, MSX, and Tandy computers, and Atari, Nintendo, and Sega game...

MacTX is a Memotech MTX512 emulator for the Mac OS.

Here is a minitel emulator for macs. Minitel is a videotext system that is very popular here in France, but is probably less well known elsewhere. This emulator is a US (English) version and says "distribute freely." Richard...

Vectorama is an emulator of several vector graphic-based arcade games, including Asteroids (Classic and Deluxe), Battlezone, Black Widow, Gravitar, Lunar Lander, Red Baron, Space Duel, and Tempest.

PalmPilot emulator

Dolphin is a GameCube and Wii emulator with high compatibility across the majority of titles for both platforms. It was first developed as closed source in 2003, and as open source since 2008. Official site