Oracle Virtualbox is a (now) free Virtualization program from Oracle.
Who made it? Originally it was developed by a company named “Innotek”.
What is it? A virtualization program is a program that allows you to run one or more guest virtual computers inside one physical computer. This feet is accomplished by emulating in software (nowadays with support built into the hardware, or the CPU) a closed environment that allows to install a new operating system inside a “sandbox” (not affecting the host operating system in any way, but able to interact with it)
What is it good for? In the past, virtualization was mostly used for experimentation in a safe environment as well as for compatibility purposes (running programs designed for older operating systems under a modern one). However, the use of virtualization has evolved greatly over the past 5 years, and now it is being used to cut costs in server based environments. A company can now run multiple and secure virtual servers under one physical server thus saving money on electricity, hardware, and maintenance. The more physical memory and physical CPU cores you have, the more virtual machines you can run without risking a crash.
What makes it better than other virtualization programs? Not much. Actually VMware, the commercial product that is it’s direct competitor, is a bit better in some aspects and is considered faster. But.. Virtualbox is free. As long as you have a CD image of the operating system you want to install along with a CD key (if required), all you need is an internet connection.
What do regular people use it for? Most probably, retro-gaming, or running old programs that no longer work under windows vista/7/8. Also, if you have an old backup CD/DVD that you suspect has a virus, it would be much safer to run it under a virtual system where it cannot damage your Host (real) Operating System. Also, people use virtualbox to run windows software on non-windows systems (MS Office on Mac or Linux).
Limitations? Having a virtual machine running inside your computer means it is inherently slower than your real machine. All the functions it performs are emulated in real-time, and that takes power and memory. Also, not all the functions are available for the virtual machine. For instance: 3d capabilities are very limited. Your spankin’ new video card will not show in your virtual machine and therefore, “heavy” or demanding games will most probably not run, or run quite slowly. Also, as the machine relies on your computer resources, it will bog down your computer if you feed it with too much memory or too much CPU power. Which means, it has the potential to crash your PC operating system. (Blue screen anyone?)
Free Alternatives? If you have Windows 7 Professional or Ultimate, you can download (for free) an add-on called “xp-mode” which installs another variation of a Windows XP virtual machine on your computer, and lets you run programs inside an xp virtual machine almost seamlessly. It’s far from perfect but a great quickfix for people who just need to run their old game and don’t want to mess around with lots of settings. VMware has a free product called “VM Player” for running existing virtual machines, and you can download a trial version of their lead home product “VM Workstation” for a 30 days trial. Another VM option is the now old-ish product “VM Server” which you can download for free for personal use, but was last updated in 2009. There are other trial options such as “Citrix XenDesktop” or the old “Microsoft Virtual PC 2007“
In any case, the virtual machine is a great idea and a valuable piece of software. And as one of the best (and free) virtualization solutions out there, I would give Virtualbox a try at least.