Do I need to learn a new language?

No. CrossFly apps are written in standard Java. If you know the Java API, you already know how to build with CrossFly — same syntax, same tooling, same ecosystem.

How is it different from Flutter or React Native?

CrossFly keeps you in Java (no Dart, no JS), runs on a LibGDX GPU rendering core for exceptional performance, and targets Android, iOS, Desktop (Windows, macOS and Linux) and the web (Chrome, Firefox, Safari and other browsers) from one codebase.

Which platforms can I target?

Android, iOS, Desktop (Windows, macOS, Linux) and the web (Chrome, Firefox, Safari and other browsers) — all compiled from the same Java source with a single build command.

Is CrossFly really open source?

Yes. The framework is open source under the Apache 2.0 license and free forever. Paid plans add support and team tooling, not core features.

Can I reuse existing Java libraries?

In most cases, yes — you have access to the Java ecosystem you already rely on, which is a major advantage over Dart- or JS-based frameworks.

How fast can I get started?

About a minute. Install the SDK, write a Window class, and run — your first multiplatform app is live before your coffee gets cold.

One Hello.java → Android · iOS · Windows · macOS · Linux · Web

iOS. Android. Desktop. Web.
From one Java file.

Write in Java with the CrossFly API and take the same code to all four platforms — Android, iOS, the web in Chrome, Firefox, Safari and other browsers, and the desktop on Windows, macOS and Linux. Truly native apps, no rewrites.

Build your first app — 60s See the benchmarks

Hello.java0.9s build

package app.hello;import dev.crossfly.ui.*;import dev.crossfly.ui.layout.*;public class Hello extends Window {  public void onAdd(boolean first) {    setLayout(new GridLayout(Position.CENTER, Position.CENTER));    add(.8f, new Label("Hello, CrossFly! ✈"));    add(.8f, new Button("Tap me")        .onAction(c -> toast("Native on every screen")));▍  }}

Android

iOS

Desktop

Web

Hello,
CrossFly! ✈

Tap me

LIVE

Redmi Note 10 Pro · 3 iterations per phaseFlashlight 0.18.0

Frame rate · cards

higher is better

CrossFly118.8*

Kotlin Multiplatform103.1

React Native75.4

.NET MAUI74.0

Flutter49.0

* at the cap · 120 Hz

Peak memory, worst scene

lower is better

CrossFly135 MB

.NET MAUI203 MB

Kotlin Multiplatform227 MB

Flutter286 MB

React Native591 MB

APK · unshrunk

lower is better

CrossFly5.95 MB

Kotlin Multiplatform6.17 MB

Flutter22.65 MB

React Native29.69 MB

.NET MAUI37.34 MB

SQLite · 100k inserts

lower is better

CrossFly216 ms

Flutter251 ms

.NET MAUI1248 ms

React Nativevalidation failed

Kotlin Multiplatformno SQLite phase

Built on tech you trust

JavaLibGDXAndroidiOSWindows · macOS · LinuxWeb

Why CrossFly

Everything you need. Nothing you have to relearn.

A complete native UI toolkit — windows, layouts, fields, styles — driven entirely from Java.

Pure Java, end to end

Write your whole app — UI, logic, navigation — in Java. No DSL, no second language, no context switching.

Performance that flies

A LibGDX rendering core delivers native-grade speed and frame rates the alternatives can only envy.

One codebase, 4 targets

Android, iOS, Desktop (Windows, macOS and Linux) and the web (Chrome, Firefox, Safari and other browsers) from a single source. Build once, ship to every screen your users own.

You already know it

If you know the Java API, you already know CrossFly. Reuse the muscle memory of millions of developers.

Native UI toolkit

Windows, TextFields, Buttons, GridLayout, styles, shadows and Material Icons — ready out of the box.

Instant feedback

Sub-second builds and a running app in under a minute keep you in flow instead of waiting.

No surprises

Crystal clear: what CrossFly is — and what it isn't

What CrossFly is

A GPU-native UI engine

Your screens draw straight through LibGDX to the GPU — real, accelerated rendering, not a web view.

100% shared code — UI included

One Java codebase covers logic and interface across Android, iOS, Desktop (Windows, macOS and Linux) and the web (Chrome, Firefox, Safari and other browsers). No platform forks.

Open to the Java ecosystem

Pull in the libraries, tools and patterns you already trust. Mix in native widgets and APIs when you need them.

A complete toolkit

Components, layouts, styles, build tooling and a simulator — everything to go from idea to store.

What CrossFly is not

Not an HTML5 wrapper

CrossFly compiles to native targets and renders on the GPU — it never ships your UI inside a browser shell.

No JavaScript bridge

There's no serialized bridge between your code and the screen, so there's nothing to become the bottleneck.

Not a new language to learn

No Dart, no JSX, no DSL. If you write Java, you're already productive on day one.

Not just native bindings

Beyond thin wrappers over platform widgets, the UI layer is truly cross-platform for real code reuse.

How it works

From zero to running in three steps

Install the SDK

Grab CrossFly with a single command. No heavy toolchain to assemble.

$ curl crossfly.dev/up | sh

Write a Window

Extend Window, drop in your components, and lay them out in Java.

public class App extends Window { }

Run anywhere

One command builds and launches on the target of your choice.

$ crossfly run --target all

Developer experience

Stay in flow. Ship faster.

The whole loop — edit, see, debug — lives inside the IDE you already use, with feedback measured in milliseconds.

Hot reload

Save your Java and watch the running app update instantly — no full rebuild, no lost state.

Live style reload

Tweak a style and the simulator reflects it on the spot, so design iteration never breaks your flow.

Your IDE, your way

First-class support in IntelliJ, Eclipse, VS Code and NetBeans — debuggers, refactors and all.

Built-in simulator

Run and debug on a device simulator straight from the IDE, no native toolchain juggling.

New

Code with an AI pair, right in your editor

Describe a screen in plain language and let CrossFly's assistant scaffold the Window, layout and styles — pure Java you can read and own.

LoginScreen.java

// "a centered login with logo + button"

class LoginScreen extends Window {

add(new Logo());

add(new TextField("user"));

add(new Button("Sign in"));

}

Performance

Performance that feels unfair.

One rendering core, drawn straight to the GPU. Measured against four frameworks on one phone, it holds the lowest memory floor and the lowest ceiling of the five.

132 MB

for 2400 text fields

2.66 MB

release APK, shrunk

216 ms

100 000 SQLite rows

Peak memory, worst scenelower is better

CrossFly135 MB

.NET MAUI203 MB

Kotlin Multiplatform227 MB

Flutter286 MB

React Native591 MB

Measured on one device across five frameworks. The full tables, and everything that qualifies them, are on the benchmark page.

The comparison

How CrossFly stacks up

	CrossFly	Codename One	Kotlin MP	Flutter	React Native
Language	Java	Java / Kotlin	Kotlin	Dart	JS / TS
Learning curve	Already know it	Java-friendly	New language	New language	New paradigm
Rendering core	LibGDX · GPU	Lightweight widgets	Native / Compose	Skia	JS bridge
Shared UI code	100%	100%	Opt-in	100%	Partial
Mobile + Desktop	All in one	All in one	Yes	Partial	Plugins
Build setup	One CLI	Cloud build	Gradle	Gradle / CLI	Node / CLI
Java ecosystem	Full access	Full access	JVM only	No	No

Pricing

Open source at the core

Start free, forever. Upgrade only when you need a team behind you.

Community

Freeforever

The full open-source framework. Everything you need to ship.

All platforms

Full UI toolkit

Community support

Apache 2.0 license

Start building

POPULAR

Pro

$19/ dev · mo

For teams that want priority support and pro tooling.

Everything in Community

Priority support

Hot-reload tooling

Private build agents

Start free trial

Enterprise

Custom

SLA, training and dedicated engineering for large orgs.

Everything in Pro

Dedicated SLA

On-site training

Custom integrations

Contact sales

FAQ

Questions, answered

Ready for take-off?

Your first multiplatform app is one minute away. If you know Java, you already know how this ends.

Get started free

iOS. Android. Desktop. Web.From one Java file.

Everything you need. Nothing you have to relearn.

Pure Java, end to end

Performance that flies

One codebase, 4 targets

You already know it

Native UI toolkit

Instant feedback

Crystal clear: what CrossFly is — and what it isn't

What CrossFly is

What CrossFly is not

From zero to running in three steps

Install the SDK

Write a Window

Run anywhere

Stay in flow. Ship faster.

Hot reload

Live style reload

Your IDE, your way

Built-in simulator

Code with an AI pair, right in your editor

Performance that feels unfair.

How CrossFly stacks up

Open source at the core

Questions, answered

Ready for take-off?

iOS. Android. Desktop. Web.
From one Java file.