The Hercules System/370, ESA/390, and z/Architecture emulator

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, NT, 2000, and XP), Solaris, FreeBSD, and Mac OS X (10.3 and later).

The installation instructions will aid you in setting Hercules up.