Most GNU/Linux distributions provide GNU Emacs in their repositories, which is the recommended way to install Emacs unless you always want to use the latest release.
GNU Emacs development is hosted on savannah.gnu.org.
apt-getto install it:
$ sudo apt-get install emacs
$ sudo dnf install emacs
The reason for GNU Emacs's existence is to provide a powerful editor for the GNU operating system. Versions of GNU, such as GNU/Linux, are the primary platforms for Emacs development. However, GNU Emacs also comes with support for some other systems, even proprietary systems that volunteers choose to support.
MSYS2 users can install Emacs (64bits build) with the following:
pacman -S mingw-w64-x86_64-emacsFor the 32bits build, evaluate:
pacman -S mingw-w64-i686-emacs
Emacs can be installed on OS X using Homebrew.
$ brew install emacs --with-cocoa
$ sudo port install emacs-app
The Emacs for OSX website also provides universal binaries.