VirtualBox - free open-source virtual machine
Linux people probably already use this thing like crazy - https://www.virtualbox.org/ - but it also runs on Windows and Mac.
It's not just for work - it's also very good for trying out all different kinds of flavors of Linux. It's much less hassle than booting directly into a Live CD/DVD, because you still have your original OS usable at all times, and also doesn't make any changes to your system like Wubi does.
Re: VirtualBox - free open-source virtual machine
Its also much easier to use than VmWare Player, and you do not have to sign up for anything.
Re: VirtualBox - free open-source virtual machine