Cross-Platform Productivity App Development

I'm looking for a skilled mobile application developer to create a productivity tool available on both iOS and Android platforms.

Essential features include:
- Task management
- Calendar integration
- File sharing

Ideal candidates should have:
- Proven experience in developing productivity apps
- Strong knowledge of both iOS and Android development
- Expertise in UI/UX design for seamless user experience
- Ability to integrate third-party APIs

Please provide a portfolio showcasing similar projects.