86Box vs Hercules

86Box is a free emulator for x86-based IBM PC systems and compatibles, covering machines from 1981 through PCI-bus systems. It emulates processors from the 8086 through the Pentium with an emphasis on accuracy and supports configurable machines such as the IBM PC 5150 and IBM PS/2 line. Users can select video adapters, sound cards, network adapters, hard-disk controllers, and SCSI adapters. Supported guest systems include MS-DOS, older Windows releases, OS/2, many Linux distributions, BeOS, and NEXTSTEP. MIDI output can use Windows MIDI support, FluidSynth, or emulated Roland synthesizers. 86Box runs on Windows, Linux, and macOS and is released under the GNU General Public License version 2 or later. The project offers stable and experimental builds; experimental versions may be less stable or slower. Most emulation logic runs in one thread, so results depend on host and guest configuration. A BIOS is required. The project recommends manager applications for multiple virtual machines, while its built-in manager is still a preview.

Hercules is a free, open-source emulator for IBM System/370, ESA/390, and 64-bit z/Architecture mainframes. It lets a PC execute programs designed for those systems and represents mainframe I/O devices with PC resources, including DASD files and local tn3270 sessions. It does not provide an operating system, so users must supply one or run a standalone program. With legally licensed software, it can run z/OS, z/VM, z/VSE, OS/390, VM/ESA, VSE/ESA, and older related IBM operating systems. Features include dynamic reconfiguration, an integrated console, interpretive execution, debugging tools, and snapshots and restore. Guest TCP/IP networking can connect to the host through TUN/TAP and hercifc, and multiple instances can share devices. Hercules is licensed under the Q Public Licence and runs on Linux, macOS, and Windows; the host list also names Solaris and FreeBSD. Documented unsupported areas include ESCON, FICON, PR/SM, coupling links, and several z/Architecture facilities. Its FAQ says it has not claimed production capability and was intended as a system programmer's toy.