Emulators

JavaScript Machines several old PC simulators.

ES40 Emulator Project portable emulator for the HP (DEC, Compaq) AlphaServer ES40.
SIMH or SIMH implements simulators for:

• Data General Nova, Eclipse
• Digital Equipment Corporation PDP-1, PDP-4, PDP-7, PDP-8, PDP-9, PDP-10, PDP-11, PDP-15, VAX
• GRI Corporation GRI-909, GRI-99
• IBM 1401, 1620, 1130, 7090/7094, System 3
• Interdata (Perkin-Elmer) 16b and 32b systems
• Hewlett-Packard 2114, 2115, 2116, 2100, 21MX, 1000
• Honeywell H316/H516
• MITS Altair 8800, with both 8080 and Z80
• Royal-Mcbee LGP-30, LGP-21
• Scientific Data Systems SDS 940

TS10 now is multi-system emulator system that includes three working emulators: PDP-10 (KS10 and KL10), PDP-11 (KDF11 and KDJ11), and VAX (MicroVAX II and VAXserver 3900).
The Hercules System/370, ESA/390, and z/Architecture Emulator See Jay Maynard - IBM Public Domain Software Collection for (links to) several Operating Systems to run on Hercules.
Project GreenPea aims to implement an emulator for the PDP-12 minicomputer.
Desktop CYBER Emulator
Oberon RISC Emulator see Project Oberon
Bochs is a highly portable open source IA-32 (x86) PC emulator written in C++, that runs on most popular platforms. It includes emulation of the Intel x86 CPU, common I/O devices, and a custom BIOS. Bochs can be compiled to emulate many different x86 CPUs, from early 386 to the most recent x86-64 Intel and AMD processors which may even not reached the market yet.
GXemul is a framework for full-system computer architecture emulation.

Mini vMac
ARDI Macintosh emulators.