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, Solaris, FreeBSD, and Mac OS X.
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. A dedicated crew of programmers is constantly at work implementing new features and fixing bugs.
"My pc thinks it's a MAINFRAME!". This is the mainframe, you still need an operating system like MVS or z/OS to run job's and applications like a true IBM mainframe. You can use the Hercules to learn mainframe assembler with z/Architecture Principles of Operation from IBM site. Not easy to a begginer to start using it. You will still need wc3270 to access zOS. Truly amazing stuff!
Fast and simple.
A nice emulator to get old (and new) large iron software (called mainframe software) running on a PC or Mac.