The Raspberry Pi is a credit-card sized computer that plugs into your TV and a keyboard. It can be used for many of the things that your desktop PC does, like spreadsheets, word-processing and games. It also plays high-definition video.
I personally use it as a backup server (pulls data from several locations using rsnapshot and backs up to a NAS) and another one as a router (added a usb to ethernet adapter and it works pretty well) and both running raspbian, so whatever you decide to do with it you’ll need to install an OS first, here are the top 6:
1. Raspbian
Raspbian is a free operating system based on Debian optimised for the Raspberry Pi hardware. An operating system is the set of basic programs and utilities that make your Raspberry Pi run. However, Raspbian provides more than a pure OS: it comes with over 35,000 packages, pre-compiled software bundled in a nice format for easy installation on your Raspberry Pi.
The initial build of over 35,000 Raspbian packages, optimised for best performance on the Raspberry Pi, was completed in June of 2012. However, Raspbian is still under active development with an emphasis on improving the stability and performance of as many Debian packages as possible.
2. Risc OS
RISC OS is a computer operating system designed in Cambridge, England by Acorn. First released in 1987, its origins can be traced back to the original team that developed the ARM microprocessor. RISC OS is owned by Castle Technology Ltd. Risc OS Open Limited (ROOL) manages the source code for this operating system.
3. Plan 9
Plan 9 is an operating system kernel but also a collection of accompanying software. The bulk of the software is predominantly new, written for Plan 9 rather than ported from Unix or other systems. The window system, compilers, file server, and network services are all freshly written for Plan 9. Although classic Unix programs like dc(1), ed(1), and even troff(1) have been brought along, they are often in an updated form. For example, troff accepts Unicode documents encoded in UTF-8, as does the rest of the system.
Developed at Bell Labs starting in the late 1980s, its original designers and authors were Ken Thompson, Rob Pike, Dave Presotto, and Phil Winterbottom. They were joined by many others as development continued throughout the 1990s to the present.
Plan 9 has had four major releases over its lifetime, released in the years 1992, 1995, 2000 and 2002 respectively.
4. Android
The operating system that powered over 85 per cent of the smartphones we use today is also a good choice for running a Raspberry Pi board. It’s open source nature and wide variety of features makes it useful for a number of purposes and gives a Pi much more power than it would usually have.
5. Arch
Arch Linux ARM is a distribution of Linux for ARM computers. We provide targeted kernel and software support for soft-float ARMv5te, and hard-float ARMv6 and ARMv7 instruction sets on a variety of consumer devices and development platforms.
Arch Linux ARM carries forward the Arch Linux philosophy of simplicity and user-centrism, targeting and accommodating competent Linux users by giving them complete control and responsibility over the system. Instructions are provided to assist in navigating the nuances of installation on the various ARM platforms; however, the system itself will offer little assistance to the user.
6. Openelec
Open Embedded Linux Entertainment Center, or OpenELEC (http://www.openelec.tv) for short, is a small Linux distribution built from scratch as a platform to turn your computer into a complete XBMC media center (http://www.xbmc.org). OpenELEC is designed to make your system boot as fast as possible and the install is so easy that anyone can turn a blank PC into a media machine in less than 15 minutes.