The Unraid Community Applications plugin is a plugin that gives you access to a wide range of useful plugins and containers all in one place. The Community Applications plugins is great for quick and easy install of other plugins, containers and applications.
Copy the following link https://raw.githubusercontent.com/Squidly271/community.applications/master/plugins/community.applications.plg and paste it into the Plugins > Install Plugin page of your Unraid install and then press the Install button.
This will now add an "APPS" tab where you can access hundreds of community applications.
Some of the more popular applications like Sonarr, Radarr and Plex are available to install from the Community Applications plugin.