Bootstrap Zero - Open-source, free Bootstrap templates collection.
AbTest.io - A free url shortener with A/B testing features
Bootstrap Magic - Create your Bootstrap 4.0 themes easily with magic
Anboto - Anboto provides web customer service and e-Commerce technology based on semantics and natural language processing.
Material Design for Bootstrap 4 - Powerful and free UI KIT for the newest Bootstrap 4 and Material Design
GoodUI Evidence - People's A/B test results that show which UI ideas work best