Bulma - Bulma is an open source CSS framework based on Flexbox and built with Sass. It's 100% responsive, fully modular, and available for free.
Streaks Workout - The personal trainer that you actually want to use.
Material UI - A CSS Framework and a Set of React Components that Implement Google's Material Design
Daily Yoga - 50+ yoga classes, 400+ workout poses, w/ HD video and music
Milligram - A minimalist CSS framework
cure.fit - At-home fitness app for strength, cardio, dance and yoga