Develop a comprehensive plan for creating a mobile application from scratch. Include the following aspects: 

1. **Concept Development**: Describe the problem the app will solve and the target audience. 
2. **Market Research**: Identify existing competitors and outline unique features that will make the app stand out. 
3. **Design**: Provide a basic wireframe layout and user interface design principles to be applied. 
4. **Technology Stack**: Specify the programming languages, frameworks, and tools needed for development.
5. **Development Process**: Outline the agile development phases, including timelines and milestones.
6. **Testing and Launch Strategy**: Discuss how you will test the app for bugs and gather user feedback before the official launch. 
7. **Marketing Plan**: Propose strategies for promoting the app post-launch. 

Make sure to include any challenges that may arise during the development process and potential solutions.