Cross-Platform Mobile Productivity App Development

I'm seeking a skilled app developer to create a mobile productivity tool. This app should be compatible with both iOS and Android platforms.

Key Requirements:
- Expertise in cross-platform mobile app development
- Experience in creating productivity tools is a plus
- Proficiency in developing apps for both iOS and Android
- Familiarity with the latest mobile app development technologies
- Experience with cloud services for seamless data synchronization and backup solutions.
- Ability to integrate third-party APIs for extended functionalities such as calendar sync and task management.
- Experience in implementing push notifications to keep users informed and engaged.
- Knowledge in securing user data with encryption and secure authentication methods.

The ideal candidate will have a keen understanding of what makes a productivity app effective and user-friendly.

Preferably developed using React Native.