KEGS is an actively-developed Apple IIgs emulator, originally written for HP workstations, improved and customized for Linux. It runs under X at any display depth, and supports changable memory sizes, joysticks, and sound. KEGS boots all Apple II OS variants, and supports all of the graphics modes of the Apple IIgs. It requires a copy of the Apple II system ROMs. Kegs has been adapted to work under Mac OS X, Windows, and the SDL library.
VICE is a Versatile Commodore Emulator, i.e. a program that runs on a Unix, Win32, MS-DOS, Mac OS X, Amiga, or RiscOS machine and executes programs intended for the old 8-bit Commodore computers. The current version emulates the C64, C128, VIC20, Plus4, C64-DTV, all the PETmodels, and the CBM-II (aka C610).
XRoar is a cross-platform emulator for the Dragon 32, Dragon 64, and Tandy CoCo computers, all originally released in the early '80s. The emulator runs under Unix-like operating systems (including Mac OS X) and Windows, with older versions available for handhelds like the Nintendo DS and GP32.
The Free Unix Spectrum Emulator (Fuse) is an emulator of the 1980s home computer and various clones. It emulates the Spectrum 16K, 48K, 128K, +2, +2A, +3, +3e, and SE, the Timex TC2048 and TC2068, the Pentagon, and the Scorpion. Almost all the common Spectrum emulator file formats are supported, including .rzx input recordings, .tzx tape images, and .szx and .z80 snapshots.
Mini vMac emulates a Macintosh Plus, one of the earliest of the Macintosh computers. It can run old Macintosh software that otherwise couldn't be used on recent machines. Mini vMac requires a ROM image file to run, and so can be legally used only by those who own a Macintosh Plus.