Emacs Lisp Package Archives (ELPA)

• http://elpa.gnu.org/ – GNU Emacs Lisp Package Archive
• http://melpa.org – Milkypostman’s Emacs Lisp Package Archive
• http://melpa.org/#/getting-started

I first came across MELPA through jira-markup-mode:

• http://melpa.org/#/jira-markup-mode
• https://github.com/mnuessler/jira-markup-mode