Emacs package managers

Starting with Emacs 24, package.el is included with Emacs which provides a built-in package manager.

You can list packages:

M-x package-list

And install packages:

M-x package-install [RET] org

Out-of-the-box the only supplied Emacs package repository is the official ELPA (Emacs Lisp Package Archive), however it does not have that many packages.

The two most popular unofficial repositories appear to be marmalade and MELPA, which is the larger of the two.

It is simple to add them both into Emacs:

M-: (add-to-list 'package-archives '("marmalade" . "https://marmalade-repo.org/packages/"))
M-: (add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/"))
M-x package-refresh-contents [RET]

Once this has been done, you will find Emacs lists thousands more packages than before. If you attempt to install a package and Emacs finds different versions of it available on the different available repositories, you will be prompted to pick the appropriate one (as of Emacs 24.2).