Designing and building a mobile application involves several steps:

1. Define the purpose and goals of your app: Start by determining the purpose of your app and what you want it to accomplish. Consider your target audience and what they will be using the app for.

2. Sketch out your app's flow and features: Next, sketch out the flow of your app and the features it will include. This will help you visualize how the app will work and what screens and functionality it will need.

3. Create wireframes and prototypes: Use wireframes and prototypes to test out different design and layout ideas for your app. This will help you refine the user experience and ensure that the app is intuitive and easy to use.

4. Choose a development platform: There are several platforms you can use to build a mobile app, including native platforms like iOS and Android, as well as cross-platform tools like Flutter and React Native. Choose the one that best fits your needs and resources.

5. Build and test your app: Use the chosen development platform to build and test your app. This will involve writing code, integrating any necessary APIs and services, and testing the app on various devices to ensure it is stable and performs well.

6. Launch and promote your app: Once your app is complete, you can launch it on the App Store or Google Play Store. To promote your app, consider creating a marketing plan that includes tactics like social media marketing, app store optimization, and influencer outreach.

There are several low-code or no-code platforms that can be used to develop mobile apps without writing code:

• Appy Pie: This platform allows you to build native iOS and Android apps using a drag-and-drop interface and pre-designed templates.

• BuildFire: BuildFire is a platform that allows you to create custom mobile apps using a range of templates and features, including push notifications, in-app messaging, and location-based services.

• GoodBarber: GoodBarber is a platform that enables you to create native iOS and Android apps using a range of templates and customization options. It also includes features like offline support, automatic updates, and integrations with popular services like Google Maps and PayPal.

• Mobile Roadie: Mobile Roadie is a platform that allows you to create and manage native iOS and Android apps using a range of templates and customization options. It also includes features like in-app purchasing, push notifications, and integrations with popular services like Facebook and Twitter.

• Shoutem: Shoutem is a platform that enables you to create native iOS and Android apps using a range of templates and customization options. It also includes features like push notifications, in-app messaging, and integrations with popular services like Facebook and Google Maps.

Keep in mind that while these platforms can be helpful for building simple apps, they may not have the capabilities or flexibility to handle more complex app development projects. It's always a good idea to carefully consider your needs and goals before choosing a development platform.

There are several open-source no-code platforms that can be used for mobile app development:

• Appery.io: This platform is based on the Apache Cordova framework and allows you to build native iOS and Android apps using a drag-and-drop interface and pre-designed templates.

• Bubble: Bubble is a platform that enables you to build custom web and mobile apps using a visual interface and pre-designed templates. It supports the development of native iOS and Android apps using Apache Cordova.

• Glide: Glide is a platform that allows you to create custom mobile apps using Google Sheets as a backend. It enables you to build native iOS and Android apps using a drag-and-drop interface and pre-designed templates.

• Thunkable: Thunkable is a platform that enables you to create custom mobile apps using a visual interface and pre-designed templates. It supports the development of native iOS and Android apps using Apache Cordova.

• AppSheet: AppSheet is a platform that enables you to create custom mobile apps using a visual interface and pre-designed templates. It supports the development of native iOS and Android apps using Apache Cordova.

It's important to note that while these platforms can be helpful for building simple apps, they may not have the capabilities or flexibility to handle more complex app development projects. It's always a good idea to carefully consider your needs and goals before choosing a development platform.