Virtualization on Apple Hardware

Possibilities to allow multiple OSes to run at the same time:

• VirtualBox - currently free.
• VMWareFusion - currently CS has a license for teaching.
• Parallels http://www.parallels.com/ - as of 2013 that seemed the fastest (on MacOSX 10.8 - 10.10); it costs about $50 per machine.

If you only need the option of multiple OSes at boottime, then BootCamp can do that.