Free MCS-51 Simulators:
*The 8051 Machine - Windows -
http://www.jroweb.de/8051/
-circa. 2002
*JSIM-51 - Windows -
http://web.archive.org/web/20160413014254/http://home.arcor.de:80/jensaltmann/jsdl/jsim-e.htm
-circa. 2000
*ucsim - DOS and Linux (no TUI) - used by sdcc -
http://mazsola.iit.uni-miskolc.hu/~drdani/embedded/s51/
-circa. 2017
*emu8051:
http://www.hugovil.com/projet.php?proj=emu8051&lang=en_US
-circa. 2014
*Tiny8051 (Windows only):
https://sourceforge.net/projects/tiny8051/
-circa. 2016
*gsim51 (command-line):
http://gsim51.sourceforge.net
-circa. 2013
*Emu51:
http://emu51.sourceforge.net
-circa. 2004
*SiMiKON - GUI using qt -
http://web.archive.org/web/20050127071817/http://simikon.sourceforge.net:80/
-circa. 2000
*Yasmin - GUI using qt - simulates at assembly code level -
http://web.archive.org/web/20050213004340/http://yasmin.sourceforge.net:80/
-circa. 2000
*MCU 8051 IDE - GUI - Lin & Win -
http://mcu8051ide.sourceforge.net
-circa. 2012