Top 10 Open Source Cross-Platform App Building Frameworks

1. Flutter

• Developed by: Google
• Programming Language: Dart
• Description: Flutter is a popular open-source framework for building natively compiled applications for mobile, web, and desktop from a single codebase. Its hot-reload feature allows developers to see changes instantly. It offers a rich set of pre-built widgets for efficient UI creation.
• Pros: Fast development, native-like performance, single codebase for multiple platforms, strong community support.
• Cons: Limited support for platform-specific features, larger app size.

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2. React Native

• Developed by: Meta Platforms (formerly Facebook)
• Programming Language: JavaScript
• Description: React Native is an open-source framework that uses JavaScript and React to build mobile apps. It features reusable components, simplifying development for iOS and Android. It also offers a live reload feature.
• Pros: Reusable code, large community support, hot-reload feature.
• Cons: Limited support for complex UIs, performance issues with complex animations.

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3. Ionic

• Developed by: Max Lynch and Ben Sperry
• Programming Language: HTML, CSS, JavaScript
• Description: Ionic is an open-source framework that uses web technologies (HTML, CSS, and JavaScript) to build cross-platform mobile apps. It provides a library of pre-built UI components and integrates with frameworks like Angular, React, and Vue.js.
• Pros: Uses familiar web technologies, rich UI component library, integrates with popular frameworks.
• Cons: Relies on plugins for native functionality, performance can be lower than native apps.

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4. NativeScript

• Developed by: Progress
• Programming Language: JavaScript, TypeScript
• Description: NativeScript is an open-source framework for building truly native mobile apps using JavaScript or TypeScript. It provides direct access to native APIs without needing third-party plugins.
• Pros: Native performance, direct access to native APIs, flexible language support.
• Cons: Smaller community, steeper learning curve.

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5. Kotlin Multiplatform

• Developed by: JetBrains
• Programming Language: Kotlin
• Description: Kotlin Multiplatform is an open-source technology that allows code sharing across platforms while retaining the benefits of native programming. It enables developers to reuse code, write native code when needed, and seamlessly integrate shared Kotlin code into any project.
• Pros: Code reusability, native performance, seamless integration.
• Cons: Relatively newer framework, smaller community compared to others.

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6. Tauri

• Developed by: Open-source contributors (managed by the Tauri community)
• Programming Language: Rust + JavaScript/HTML/CSS
• Description: Tauri is a lightweight framework for building desktop applications with web technologies. It focuses on providing smaller application sizes and tighter security compared to Electron.js by leveraging Rust for backend processes and WebView for the frontend.
• Pros: Extremely small app sizes, enhanced security, cross-platform support (Windows, macOS, Linux).
• Cons: Relatively new framework with a smaller community, limited to desktop apps.

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7. Electron.js

• Developed by: OpenJS Foundation (initially by GitHub)
• Programming Language: JavaScript, HTML, CSS
• Description: Electron.js allows developers to build desktop applications using web technologies. It bundles Chromium and Node.js, offering a single codebase to create cross-platform apps.
• Pros: Extensive community, support for multiple platforms, access to Node.js APIs.
• Cons: Large app sizes due to bundling Chromium, performance overhead compared to native apps.

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8. Qt for Python (PySide)

• Developed by: The Qt Company
• Programming Language: Python
• Description: Qt for Python (also known as PySide) is a set of Python bindings for the Qt framework, enabling developers to create cross-platform applications with a focus on rich graphical interfaces.
• Pros: High-performance UI, cross-platform support, versatile tools for both desktop and mobile.
• Cons: Steeper learning curve, complex debugging for Python-Qt integrations.

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9. Apache Cordova

• Developed by: Apache Software Foundation
• Programming Language: HTML, CSS, JavaScript
• Description: Apache Cordova is a framework for building mobile applications using web technologies. It acts as a wrapper, allowing access to device APIs via JavaScript.
• Pros: Easy to learn for web developers, wide plugin support, cross-platform.
• Cons: Performance issues compared to native apps, reliance on plugins for advanced features.

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10. Expo

• Developed by: Expo team and community
• Programming Language: JavaScript
• Description: Expo is an open-source framework built on React Native, offering a streamlined environment to build React Native applications. It includes pre-configured libraries and tools to speed up the development process.
• Pros: Simplifies React Native development, excellent documentation, large community.
• Cons: Limited flexibility compared to plain React Native, dependency on the Expo ecosystem.

Note: The search results also mention other frameworks (Xamarin, .NET MAUI, PhoneGap, Node.js, Appcelerator Titanium, Sencha Touch, Corona SDK, Framework 7), but these are not explicitly identified as open-source in all sources. The above list focuses on those consistently presented as open-source options.