Power20 is described as 'emulator for the Commodore VIC-20. It allows you to run your favorite VIC-20 software on your Apple Macintosh (with PowerPC or intel-CPU) at full speed with smooth graphics and great sound'. There are seven alternatives to Power20 for a variety of platforms, including Mac, Windows, Linux, BSD and Haiku. The best alternative is WinUAE, which is both free and Open Source. Other great apps like Power20 are VICE (Free, Open Source), Frodo (Free), WinFellow (Free) and C64 Forever (Freemium).
VICE is a program that runs on a Unix, MS-DOS, Win32, OS/2, Acorn RISC OS, BeOS, QNX 4.x, QNX 6.x, Amiga, GP2X, Dingoo, Syllable, SkyOS or Mac OS X machine and executes programs intended for the old 8-bit computers.
Power64 - Commodore64 Emulator for the Power Macintosh. Power64 is an emulator for the Commodore C64. It allows you to run your favorite C64 software on your Apple Macintosh (with PowerPC or intel-CPU) at full speed with smooth graphics and great sound.
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.