Spaggel Tooltip is free a module to add product attribute tooltip support to Magento 2.
Download Spaggel Tooltip from GitHub OR view the demo here

Motivation
By default Magento 1 and 2 lack support for attribute tooltips. Not having tooltips is amiss and should be core functionality in my opinion.
A tooltip can make information easily accessible for customers which are not sure what some attributes (or values) mean.
I also wanted to learn more about Magento 2 modules and saw this as an opportunity to give back to the open-source community.
About the module
The tooltip module adds an extra WYSIWYG (HTML support) field to the product attribute settings to Magento 2.

I’m currently working on support for:
- CMS variables (like {{store url}})
- Adding tooltips to layered navigation
Extra information
More in-depth technical information about how the module works can be found on the GitHub wiki.
A very basic user guide is also available here.
Missing features and issues
If you experience any issues or want an extra feature (in the scope of the module) please add an issue on GitHub here.