Virtualization software for OS X. It only runs on Intel Macs.
VMware Fusion is a virtual machine software product developed by VMware for Macintosh computers with Intel processors. Fusion allows Intel-based Macs to run x86 and x86-64 "guest" operating systems, such as Microsoft Windows, Linux, NetWare and Solaris as virtual machines simultaneously with Mac OS X as the "host" operating system using a combination of paravirtualization, emulation and dynamic recompilation. -Wikipedia