Plus4

Artifex
A freeware C16 and Plus/4 emulator for Windows.
http://artifex.emuunlim.com/

C16-Plus4 Retro Page
Game downloads, computer history, tips and home of YAPE, A freeware C16 and Plus/4 emulator for Windows. An older open source version for Unix/SDL is also available.
http://yape.homeserver.hu/

Minus4
A freeware Plus/4 emulator for DOS, Java, and Windows. The Source Code for the Windows version is also available.
http://javalemmings.com/minus4/

plus4emu
An open source emulator for Linux, MacOS, and Windows.
http://sourceforge.net/projects/plus4emu/

WinEMU
A freeware C16/Plus4 emulator for DOS and Win32 platforms. Also contains game cheats and a developer section.
http://winemu.emuunlim.com/