jQuery - The Write Less, Do More, JavaScript Library.
Grav - The modern open source flat-file CMS
React Native - A framework for building native apps with React
WonderCMS - WonderCMS is the smallest flat file CMS. Completely free, open source, privacy oriented for over 12 years.
Babel - Babel is a compiler for writing next generation JavaScript.
HTMLy - HTMLy is an open source databaseless blogging platform. A Flat-File Blog and Flat-File CMS written in PHP prioritizes simplicity and speed.