Debian is a free operating system (OS) for your computer. An operating system is the set of basic programs and utilities that make your computer run. Debian uses the Linux kernel (the core of an operating system), but most of the basic OS tools come from the GNU project; hence the name GNU/Linux.
Debian GNU/Linux provides more than a pure OS: it comes with over 29000 packages, precompiled software bundled up in a nice format for easy installation on your machine.
FreeBSD is an advanced computer operating system used to power modern servers, desktops and embedded platforms. A large community has continually developed it for more than thirty years. Its advanced networking, security and storage features have made FreeBSD the platform of choice for many of the busiest web sites and most pervasive embedded networking and storage devices.
Fedora is a Linux-based operating system, a suite of software that makes your computer run. You can use the Fedora operating system to replace or to run alongside of other operating systems such as Microsoft Windows™ or Mac OS X™. The Fedora operating system is 100% free of cost for you to enjoy and share.
Raspbian is a free operating system based on Debian optimized 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.