Hercules vs QEMU

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.

QEMU is a free, open-source machine emulator and virtualizer. System emulation models an entire machine, including its CPU, memory and devices, so it can run a guest operating system. User-mode emulation runs processes built for one CPU architecture on another. The package also includes qemu-img, a command-line utility for creating, converting and modifying disk images. QEMU can work with KVM, Xen and Hypervisor.Framework so guests can run directly on the host CPU. Supported build platforms include Linux, macOS, FreeBSD, NetBSD, OpenBSD and Windows. Windows support is limited to 64-bit, while macOS requires the newest version currently available; support for the prior version is eventually dropped. For complex networking and storage configurations, the project recommends management tools such as virt-manager. Its security guidance distinguishes virtualization with an accelerator and listed machine type from TCG non-virtualization use, which does not provide guest-isolation or security guarantees. QEMU is released under GNU GPL version 2, with some components under specific licenses.