Here is the list of Eleven all time popular Linux distributions. The list is not in the order. I am not talking about good vs best. The list has been created to remind you the names.
Ubuntu : The world's most popular free OS. No, No. I am not saying this. Ubuntu's site claims this. According to wikipedia Ubuntu is a computer operating system based on the Debian Linux distribution and distributed as free and open source software, using its own desktop environment. It is named after the Southern African philosophy of ubuntu, which can be translated as "humanity towards others" or "the belief in a universal bond of sharing that connects all humanity"
Fedora : Fedora (Fedora Core) is an RPM-based operating system based on the Linux kernel. It is developed by Fedora Project which is owned by Red Hat. Source model is Free and open source software.It's Update method is based on Yum (Yellowdog updater modified) and it's Package manager is RPM (Redhat package manager).
CentOS : CentOS (Community ENTerprise Operating System) is a Linux distro which attempts to provide a free class computing platform which has 100% binary compatibility with its upstream source, RHEL-Red Hat Enterprise Linux.Source model is Free and open source software.It's Update method is based on Yum (Yellowdog updater modified) and it's Package manager is RPM (Redhat package manager).
Debian : Debian is an operating system composed of open source software packages carrying the GNU General Public License. Debian GNU/Linux operating system is made up of free software from the GNU project and of a kernel from the Linux project.Source model is Free and open source software.It's Update method is based on apt (Advanced packaging Tool) and it's Package manager is dpkg (Debian PacKaGe Management System).
LinuxMint : Linux Mint is a computer operating system based on the Linux distribution Ubuntu. Linux Mint has some installed softwares by default like Java and the Adobe Flash web browser plugin, which are not installed by default in most Linux distributions. Source model is Free and open source software.It's Update method is based on mintUPDATE & apt (Advanced packaging Tool) and it's Package manager is dpkg (Debian PacKaGe Management System).
OpenSUSE : openSUSE is a free and Linux-based operating system for your PC, Laptop or Server. It is a general purpose operating system built on top of the Linux kernel, developed by the community-supported openSUSE Project and sponsored by SUSE and a number of other companies. After Novell acquired SUSE Linux in January 2004,[4] Novell decided to release the SUSE Linux Professional product as a 100% open source project. Source model is Free and open source software.It's Update method is based on Zypp (YAST - Yet another Setup Too) and it's Package manager is RPM (Redhat package manager).
Arch Linux : Inspired by CRUX, another minimalist distribution for i686 and x86-64 computers. Source model is Free and open source software.It's Update method is based on Pacman and it's Package manager is Pacman.
Slackware : It was one of the earliest operating systems to be built on top of the Linux kernel and is the oldest currently being maintained.Slackware was originally derived from the Softlanding Linux System (SLS), the most popular of the original Linux distributions and the first to offer a comprehensive software collection that comprised more than just the kernel and basic utilities. Source model is Free and open source software.It's Update method is based on pkgtools/slackpkg and it's Package manager is pkgtools/slackpkg.
Mandriva Linux : Mandriva, S.A. is the creator and maintainer of Mandriva Linux. Mandriva, S.A. began as MandrakeSoft in 1998. The first release was based on Red Hat Linux (version 5.1) and K Desktop Environment 1 in July 1998. Source model is Free and open source software.It's Update method is based on urpmi (rpmdrake) and it's Package manager is RPM (Redhat package manager).
Gentoo : Gentoo Linux is a computer operating system built on top of the Linux kernel and based on the Portage package management system. Gentoo Linux was initially created by Daniel Robbins as the Enoch Linux distribution. Although originally built on the x86 architecture, Gentoo has been ported to many others. Currently it is officially supported and considered stable on x86, x86-64, IA-64, PA-RISC. Source model is Free and open source software.It's Update method is based on Emerge and it's Package manager is Portage.
Puppy Linux : Puppy Linux is a lightweight Linux distribution. Puppy Linux features built-in tools which can be used to create bootable USB drives, create new Puppy CDs, or remaster a new live CD with different packages. Source model is Free and open source software.It's Package manager is PetGet, Puppy Package Manager.
Ubuntu : The world's most popular free OS. No, No. I am not saying this. Ubuntu's site claims this. According to wikipedia Ubuntu is a computer operating system based on the Debian Linux distribution and distributed as free and open source software, using its own desktop environment. It is named after the Southern African philosophy of ubuntu, which can be translated as "humanity towards others" or "the belief in a universal bond of sharing that connects all humanity"
Fedora : Fedora (Fedora Core) is an RPM-based operating system based on the Linux kernel. It is developed by Fedora Project which is owned by Red Hat. Source model is Free and open source software.It's Update method is based on Yum (Yellowdog updater modified) and it's Package manager is RPM (Redhat package manager).
CentOS : CentOS (Community ENTerprise Operating System) is a Linux distro which attempts to provide a free class computing platform which has 100% binary compatibility with its upstream source, RHEL-Red Hat Enterprise Linux.Source model is Free and open source software.It's Update method is based on Yum (Yellowdog updater modified) and it's Package manager is RPM (Redhat package manager).
Debian : Debian is an operating system composed of open source software packages carrying the GNU General Public License. Debian GNU/Linux operating system is made up of free software from the GNU project and of a kernel from the Linux project.Source model is Free and open source software.It's Update method is based on apt (Advanced packaging Tool) and it's Package manager is dpkg (Debian PacKaGe Management System).
LinuxMint : Linux Mint is a computer operating system based on the Linux distribution Ubuntu. Linux Mint has some installed softwares by default like Java and the Adobe Flash web browser plugin, which are not installed by default in most Linux distributions. Source model is Free and open source software.It's Update method is based on mintUPDATE & apt (Advanced packaging Tool) and it's Package manager is dpkg (Debian PacKaGe Management System).
OpenSUSE : openSUSE is a free and Linux-based operating system for your PC, Laptop or Server. It is a general purpose operating system built on top of the Linux kernel, developed by the community-supported openSUSE Project and sponsored by SUSE and a number of other companies. After Novell acquired SUSE Linux in January 2004,[4] Novell decided to release the SUSE Linux Professional product as a 100% open source project. Source model is Free and open source software.It's Update method is based on Zypp (YAST - Yet another Setup Too) and it's Package manager is RPM (Redhat package manager).
Arch Linux : Inspired by CRUX, another minimalist distribution for i686 and x86-64 computers. Source model is Free and open source software.It's Update method is based on Pacman and it's Package manager is Pacman.
Slackware : It was one of the earliest operating systems to be built on top of the Linux kernel and is the oldest currently being maintained.Slackware was originally derived from the Softlanding Linux System (SLS), the most popular of the original Linux distributions and the first to offer a comprehensive software collection that comprised more than just the kernel and basic utilities. Source model is Free and open source software.It's Update method is based on pkgtools/slackpkg and it's Package manager is pkgtools/slackpkg.
Mandriva Linux : Mandriva, S.A. is the creator and maintainer of Mandriva Linux. Mandriva, S.A. began as MandrakeSoft in 1998. The first release was based on Red Hat Linux (version 5.1) and K Desktop Environment 1 in July 1998. Source model is Free and open source software.It's Update method is based on urpmi (rpmdrake) and it's Package manager is RPM (Redhat package manager).
Gentoo : Gentoo Linux is a computer operating system built on top of the Linux kernel and based on the Portage package management system. Gentoo Linux was initially created by Daniel Robbins as the Enoch Linux distribution. Although originally built on the x86 architecture, Gentoo has been ported to many others. Currently it is officially supported and considered stable on x86, x86-64, IA-64, PA-RISC. Source model is Free and open source software.It's Update method is based on Emerge and it's Package manager is Portage.
Puppy Linux : Puppy Linux is a lightweight Linux distribution. Puppy Linux features built-in tools which can be used to create bootable USB drives, create new Puppy CDs, or remaster a new live CD with different packages. Source model is Free and open source software.It's Package manager is PetGet, Puppy Package Manager.