B-Em, by Tom Walker, is an open source emulator of all models of the BBC Micro and uses the 2xsai library,
(shareware) Emulator Enhancer adds a number of additional features to many of the emulators available including aspect ratio correction, bilinear filtering, full screen mode and more.
a portable emulator of MSX/MSX2/MSX2+ home computers, written in C. Because of its portability, fMSX runs on many different systems including Unix, MacOS, AmigaOS, MSDOS, and Windows
Mugrat is a colecovision Emulator which includes a built-in Easter egg.
O2EM is a freeware open source multi-platform Odyssey², Videopac and Videopac+ emulator.
Vecx can run just about all the Vectrex software out there, and the Mac OS X version includes sound emulation.