Cross-Platform Utility App Development

I need an experienced app developer to create a cross-platform utility tool. The app should include:
- User authentication
- Push notifications
- Data synchronization

Ideal skills and experience:
- Proficiency in cross-platform app development (React Native, Flutter, etc.)
- Strong background in implementing secure user authentication
- Experience with push notification services
- Expertise in data synchronization techniques and technologies

Please provide a portfolio showcasing similar projects.