Cross-Platform Online Course App Development

I'm looking for a skilled developer to create a comprehensive online course platform available on iOS, Android, and Web. The platform will cater to students, instructors, and admins.

Key Features:
- Pre-recorded course videos
- Exams and quizzes
- Discussion and comments sections
- Student ranking based on results

Ideal Skills and Experience:
- Expertise in mobile and web app development
- Experience with video content integration
- Strong backend development skills for managing user roles and data
- UI/UX design experience for a user-friendly interface

Please provide your portfolio and relevant experience.