VirtualBox is free!
VirtualBox is an open-source app that allows you to create a virtual machine on your Mac so that you can run another operating system – usually a flavour of Windows – inside OS X. In that respect, it does the same job as both Parallels Desktop and VMware Fusion.
There is, of course, another free option for running Windows on your Mac: Apple’s own Boot Camp. If you only want to run Windows occasionally (and don’t mind rebooting your Mac to do it), you can use Boot Camp Assistant to create a partition on your main drive and install Windows on it. That way, when you boot up your Mac, you can hold down å and decide whether you want to run OS X or Windows. Remember that whichever option you choose, you’ll need a licensed copy of whatever OS you want to install.
Boot Camp has an advantage over all the virtualisation options in that because you’re running Windows natively, it will run more quickly and more smoothly. Take note however, that you do lose the convenience of running OS X apps simultaneously.
VirtualBox allows you to run Windows in a virtual environment, while still allowing you to use your Mac as normal.
There are a few differences between VirtualBox and Parallels Desktop, more than with most apps in this feature. For example, setting up Parallels and installing all the necessary drivers to allow you to access your Mac’s hardware and peripherals, is a very simple to do – it’s not so easy in VirtualBox. In fact, it can be rather daunting, but there’s lots of help on the website at virtualbox.org. Also, a number of benchmark tests of both applications have shown that VirtualBox lags behind Parallels Desktop in the performance stakes; it’s not really an option for playing PC games on your Mac.
If, however, you only need to use Windows occasionally (say, to use a specific application or to test how a website looks in Internet Explorer), it will serve you well. It has a strong open-source community behind it, plenty of documentation to help you if you run in to trouble, and there are plenty of active users helping out with advice in related forums too.