Hercules is an open source software implementation of the mainframe System/370
and ESA/390 architectures, in addition to the new 64-bit z/Architecture.
Hercules runs under Linux, Windows 98, Windows NT, and Windows 2000. 

Hercules was created by Roger Bowler and is maintained by Jay Maynard. Jan
Jaeger designed and implemented many of the advanced features of Hercules,
including dynamic reconfiguration, integrated console, interpretive execution
and z/Architecture support. 

WWW: http://www.conmicro.cx/hercules/