Cross-Platform Utility App Development

I'm looking for an experienced app developer to create a utility app for both iOS and Android platforms.

Essential features:
- User Authentication
- Push Notifications
- Offline Mode

Ideal skills and experience:
- Proven track record in developing cross-platform apps
- Expertise in implementing robust user authentication systems
- Experience with push notifications and offline functionality
- Strong UI/UX design skills
- Familiarity with both iOS and Android development guidelines

Please share your portfolio and relevant experience.