Tikva for Grav CMS is a minimalistic theme, based on Bootstrap 4 framework. Grav is a modern open-source flat-file content management system.
You’ll find a demo site with description of features at tikva-demo. Of course it is released as Open Source under MIT License. Have a look at the sources and further information at it’s Github pages. It was added to GPM (Grav Package Manager) on February, 22nd 2017.