Keep your site up to date and safe.
Although this is technically not a component or a plugin, it is a MUST HAVE for all Joomla websites.
is a service that you can use to perform back ups (together with Akeeba Backup), updates of the Joomla core and plugins and components, security checks, and so much more all in one service.
Your first site is for free, and after that it is very affordable and easy to use.
I highly recommend this to kep your site(s) safe, backupped and secure.