Netbeans has removed ruby support since version 7.0 . So now it do not come inbuilt with Netbeans 7.0 or 7.3 or 8.0 or any other higher version, but still available as plugin from ruby community.
You can add it with below simple steps :
=> Start your Netbeans IDE
=> Go to Tools -> Plugins -> Settings
=> Click Add on the setting page. It will open a new window for you and provide fields to enter plugin name and URL
=> Name it ruby (you can give any name you want) . within the URL provide below.
=> click O.K to complete the plugin addition
=> Now click on Available Plugins tab and search for ruby or whatever name you have given to the plugin.
=> The ruby plugin will be listed in the search, click it to select and you will see install button appear at the bottom
=> just click install and follow the instruction like accept agreement, click next etc
If you do not get next button at any stage, it may be due to some missing dependency .
Earlier I was using some other URL for the plugin
and getting below message in the installation window with the next button inactive
plugin org.netbeans.modules.web.client.tools.api is requested in version 1.0
If you face similar problem.. read this blog
=> You are done, now you can use netbeans for your Ruby development as usual…. Be Happy :)