The Nucleus framework lets you write cross-platform desktop applications using Kotlin. It is based on Compose Multiplatform and adds native window decorations, deep operating-system integration, code signing, and native installers — all configured through a single Gradle DSL. Your app runs either as a GraalVM Native Image or on the JVM.

It targets the gap between "a Compose Desktop window" and "an application the operating system treats as its own" — the work that is normally spread across a dozen half-maintained libraries and a hand-written packaging pipeline. Every OS integration is a real platform API behind a Kotlin one: no AWT dependency on the Tao backend, and the accessibility layer is verified against AT-SPI, UI Automation, and macOS AX in CI on all three platforms.

Read Why Nucleus for how it compares to Electron and Tauri.

Project status

Nucleus is under active development and moves fast. All published runtime modules run in Kotlin explicitApi() mode with their public surface locked by a binary-compatibility dump (api/*.api, checked by apiCheck via kotlinx binary-compatibility-validator). Breaking changes to a public FQN or signature fail CI. The one exception is decorated-window-jewel (JVM 25 bytecode), which still uses explicitApi() but is not dumped until BCV can read class-file major version 69. The Tao backend is the recommended one for new projects — decorated-window-jni and decorated-window-jbr are kept for existing users and receive fixes only.

Used by

• AB Download Manager — packaging plugin
• Hammer
• OtakuWorld
• Husi
• Zayit
• GitVantage

Showcase

• EdgeTranslator — offline AI translator

Installation

Nucleus ships as a Gradle plugin. Apply it alongside the Kotlin and Compose plugins in your module's build.gradle.kts:

plugins {
    kotlin("jvm") version "2.4.0"
    id("org.jetbrains.compose") version "1.11.1"
    id("dev.nucleusframework") version "2.4.4"
}

repositories {
    mavenCentral()
    google()
}

dependencies {
    implementation(compose.desktop.currentOs)
    // Entry point — provides nucleusApplication and DecoratedWindow
    implementation("dev.nucleusframework:nucleus.nucleus-application:2.4.4")
    // Tao backend — Rust-native windowing
    implementation("dev.nucleusframework:nucleus.decorated-window-tao:2.4.4")
}

For more installation options, see the install guide and project setup.

Requirements

Nucleus builds on Compose Multiplatform and requires:

Requirement	Version	Note
JDK	17+ (25+ for AOT cache)	JBR 25 recommended
Kotlin	2.4+	This repo builds with Kotlin 2.4.0
Gradle	9.0+	Bundled wrapper is Gradle 9.4.0

Platform support

Each build can compile, run, and package for macOS, Windows, and Linux from a single codebase.

• macOS — Intel (x64) and Apple Silicon (arm64), shipped as a universal binary. Liquid Glass on macOS 26.
• Windows — x64 and arm64.
• Linux — x64 and arm64, with Wayland and X11 support.

Getting started

Create src/main/kotlin/com/example/Main.kt:

package com.example

import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.material.Text
import androidx.compose.ui.Modifier
import dev.nucleusframework.application.DecoratedWindow
import dev.nucleusframework.application.nucleusApplication

fun main(args: Array<String>) = nucleusApplication(args) {
    DecoratedWindow(
        onCloseRequest = ::exitApplication,
        title = "MyApp",
    ) {
        Box(Modifier.fillMaxSize()) {
            Text("Hello from Nucleus")
        }
    }
}

nucleusApplication initializes GraalVM native-image support, takes the single-instance lock, and primes autolaunch / Windows AUMID when those modules are on the classpath. Pass the process args so deep links, file associations, and "started at login" see the original command line. The default backend is Auto (Tao if decorated-window-tao is present, otherwise AWT). Inside the block you can call onDeepLink { } and aotTraining(); plugin-injected metadata is NucleusApp, not a generated constants object.

Then configure packaging in build.gradle.kts:

nucleus.application {
    mainClass = "com.example.MainKt"

    nativeDistributions {
        packageName = "MyApp"
        packageVersion = "1.0.0"
        targetFormats(TargetFormat.Dmg, TargetFormat.Msi, TargetFormat.Deb)
    }
}

./gradlew run                              # Run locally in a native Tao window
./gradlew packageDistributionForCurrentOS  # Build an installer for your OS

The full quickstart walks through each step.

Resources for learning Nucleus

• nucleusframework.dev/en/docs — all of Nucleus's documentation
• Quickstart — build and package your first app
• Architecture — the layered model behind the framework
• examples/ — demo and sample applications, including the flagship nucleus-demo

What Nucleus provides

Ship everywhere — 18 packaging formats (DMG, PKG, EXE, MSI, NSIS, NSIS-Web, Portable, AppX, DEB, RPM, Pacman, AppImage, raw AppImage, Snap, Flatpak, ZIP, TAR, 7Z), store publishing (Mac App Store, Microsoft Store, Snapcraft, Flathub), code signing and notarization, built-in auto-update, deep links, and file associations.

Feel native — Decorated windows with native controls, notifications, taskbar/dock badges and menus, media controls (MPRIS, Now Playing, SMTC), dark mode, accent colors, global hotkeys, and system tray — all behind clean Kotlin APIs.

Perform — GraalVM Native Image compiles your app to a standalone binary with automatic reachability metadata; a typical Compose UI cold-starts in about half a second and settles around 100–150 MB of RAM. Or stay on the JVM with an AOT cache (JDK 25+) and ProGuard-optimized release builds.

Runtime modules

Each module is published independently to Maven Central — use them together or standalone.

Module	Description
nucleus.nucleus-application	nucleusApplication, backend-agnostic DecoratedWindow / HostedWindow
nucleus.core-runtime	Platform detection, single instance, deep links, NucleusApp metadata
nucleus.aot-runtime	AOT cache mode detection
nucleus.updater-runtime	Auto-update (GitHub/S3), SHA-512, delta/blockmap, progress
nucleus.darkmode-detector	Reactive OS dark mode detection
nucleus.system-color	Reactive accent color & high contrast detection
nucleus.system-info	CPU, memory, GPU (NVIDIA/AMD/Intel), temperature, network, processes
nucleus.decorated-window-tao	Recommended windowing backend (Rust tao, no AWT)
nucleus.decorated-window-core	Shared window types, layout, chrome (design-system agnostic)
nucleus.decorated-window-awt	AWT chrome shared by the JBR/JNI backends
nucleus.decorated-window-jbr	Legacy JBR backend (maintenance only)
nucleus.decorated-window-jni	Legacy JNI/AWT backend (maintenance only)
nucleus.decorated-window-jewel	Jewel (IntelliJ theme) integration
nucleus.decorated-window-material2	Material 2 integration
nucleus.decorated-window-material3	Material 3 integration
nucleus.notification-common	Cross-platform notification DSL with per-platform option blocks
nucleus.notification-macos	macOS User Notifications
nucleus.notification-windows	Windows Toast Notifications
nucleus.notification-linux	Freedesktop Desktop Notifications
nucleus.launcher-macos	macOS Dock API — badge, menus
nucleus.launcher-windows	Windows taskbar — badges, jump lists, overlay icons, thumbnail toolbar
nucleus.launcher-linux	Unity Launcher — badge, progress, urgency, quicklist
nucleus.media-control	OS media controls — MPRIS (Linux), Now Playing (macOS), SMTC (Windows)
nucleus.menu-macos	Native macOS menu bar
nucleus.freedesktop-icons	Type-safe freedesktop icon naming constants
nucleus.sf-symbols	Type-safe SF Symbols catalog
nucleus.taskbar-progress	Cross-platform taskbar progress bar & attention requests
nucleus.taskbar-progress-tao	Taskbar progress on the Tao backend
nucleus.global-hotkey	System-wide keyboard shortcuts
nucleus.energy-manager	Energy efficiency & screen-awake APIs
nucleus.autolaunch	Start the app at user login across all platforms
nucleus.scheduler	OS-scheduled background tasks (Task Scheduler / launchd / systemd)
nucleus.scheduler-testing	Test doubles for scheduler
nucleus.fs-watcher	Native filesystem watcher
nucleus.service-management-macos	macOS SMAppService — login items, launch agents, daemons
nucleus.native-ssl	OS trust store integration
nucleus.native-http	HTTP client with native SSL
nucleus.native-http-okhttp	OkHttp engine on native-http
nucleus.native-http-ktor	Ktor engine on native-http
nucleus.linux-hidpi	Native HiDPI scale detection on Linux
nucleus.graalvm-runtime	Native-image bootstrap, font fixes, automatic resource inclusion

Documentation

Full documentation is available at nucleusframework.dev (English and French).

Community

Ask questions, report bugs, and share what you're building on GitHub Discussions and the issue tracker.

License

MIT