Nucleus is a framework designed for building native desktop applications using Kotlin. It aims to provide developers with a way to create applications that are deeply integrated with the operating system, offering native behavior and performance while maintaining the simplicity and expressiveness of Kotlin. Nucleus is positioned as an evolution in desktop development, building on the JVM and Compose Multiplatform to deliver a desktop application stack that emphasizes native integration and lightweight performance.
The framework offers a unified Kotlin API that wraps complex, platform-specific native APIs, making features such as window decorations, notifications, taskbar badges, dock menus, dark mode, accent colors, global hotkeys, and system tray functionality accessible and consistent across macOS, Windows, and Linux. This API is designed to simplify the process of using native capabilities, reducing the need for developers to navigate disparate platform documentation or manage differing threading models. Nucleus exposes full platform features without resorting to lowest-common-denominator abstractions, allowing developers to leverage the complete set of native APIs in a more approachable way.
Performance is a key focus, with Nucleus leveraging the HotSpot JVM for just-in-time compilation and true parallelism, including support for real threads, coroutines, and virtual threads. For those seeking even lighter deployments, GraalVM native image support enables compilation to standalone binaries with fast cold starts and low memory usage, eliminating the need for a bundled JRE. Packaging is extensive, supporting 16 formats such as DMG, PKG, NSIS, MSI, AppX, DEB, RPM, AppImage, Snap, Flatpak, and more, facilitating distribution through various app stores and package managers. Built-in support for code signing, notarization, and auto-update is also provided.
Nucleus integrates with Compose Multiplatform for UI development, utilizing GPU-accelerated Skia rendering and a reactive state model, and supports advanced desktop UI frameworks like Jewel and Material 2/3. The framework is suitable for Kotlin developers seeking to build cross-platform desktop applications that behave as true native citizens on every operating system.
Nucleus is a Frameworks & SDKs product. It focuses on simplifying the development of native desktop applications with deep OS integration using Kotlin. It is built as an open-source project for kotlin developers building desktop apps. Nucleus is open source under the MIT license. It runs on macOS, Windows, and Linux, and it can be self-hosted.
It is developed by kdroidFilter, and the product first shipped in 2026. Development happens publicly on GitHub with 253 stars and 317 commits in the last 90 days. Key capabilities include native desktop UI, notifications, and tray integration.
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