Minix was designed initially for educational purposes by Andy Tanen Baum.An open-source operating system for x86 PCs, written in assembly language.
Rather than implement a full and heavyweight VM which can run all guest Operating Systems (OSes), the new approach is designed to run only Linux VMs, making the new plex86 architecture on the order of 10x or 100x more simplistic.
Freeware, open-source virtual Machine for Windows, Linux, MAC.
You can download versions for Linux, Windows, MAC, Risc OS, Solaris, OS/2, Be OS, Zeta.
An open source software implementation of the IBM mainframe System/370 and ESA/390 architectures, in addition to the new IBM 64-bit z/Architecture.
In this case, Mac OS is the 'host operating system', and Linux is the 'guest operating system'.
Alternatively, if you have a PC which has Windows installed, you can use e.g. Bochs is a highly portable open source IA-32 (x86) PC emulator written in C , that runs on most popular platforms.
Cross Over enables you to run Windows software on Linux, MAC OS X and Solaris without needing to have a license for Windows (legally).
This is an improved version of wine which offers enhanced compatibility with Windows.
Many pre-built freeware virtual machines are available for download here.
Note from the editor: we found it very difficult to download almost any free appliance due to server-timeout and other connection problems. Virtual platform which enables running more than one operating system simultaneously on one xxx86 computer.
Currently only available for x86 machines, but will be ported to other platforms.