IBM Mainframe

FLEX-ES
System/390 on Intel-based servers.
http://www.funsoft.com/

IBM 7094 Emulator
An open source IBM 7094 series emulator for Windows written in Delphi.
http://members.optushome.com.au/intaemul/Emul7094.htm

s709 - IBM 709/7090/7094 emulator
An open source IBM 709/7090/7094 emulator for Windows.
http://www.piercefuller.com/oldibm-shadow/709x.html

Soft390
System/390 on IA64-based servers.
http://www.platform-solutions.com