Free extensions Joomla
CSS tooltip plugin
Tooltips are a great way to show your user more information by simply hovering over an image or text.
They can be used, for example, to provide captions for images, or longer descriptions for links, or any useful information which would improve the user experience of your site, without intruding on the design.
To use, You need to give it a title which will be the tooltip content, and assign it a class: jt-tooltip