scala-ui — a thick-client UI framework for Scala

Status: research / planning. Nothing is built yet. This repository currently holds the requirements, landscape analysis, architecture options and roadmap for a Scala-native UI framework that targets Android, iOS, macOS, Windows and Linux.

Why

Scala today covers the server (JVM), the browser (Scala.js — Laminar, scalajs-react, Tyrian) and the command line (Scala Native). It has no answer for the thick client: there is no way to ship a Scala app to a phone or a desktop that looks and feels like it belongs there. Kotlin has Compose Multiplatform, Dart has Flutter, JS has React Native, C# has MAUI/Avalonia/Uno, Rust has Tauri/Slint. Scala has nothing, and that gap keeps Scala out of an entire class of products.

What this plan proposes (one paragraph)

Build a declarative, reactive UI core in pure Scala 3 (cross-compiled to JVM, JS and Native) that describes the UI as a tree, lays it out with Flexbox (Yoga), and hands each leaf to a real native widget via a thin per-platform renderer: android.view.* on Android (Scala on the JVM), UIKit/AppKit on iOS/macOS (Scala Native calling a small Swift shim with a C ABI), GTK4 on Linux (existing Scala Native bindings), WinUI/Win32 on Windows (C shim). "Looks like the platform" is therefore true by construction, accessibility comes with the native controls, and the developer writes one Scala codebase. State is reactive (fine-grained signals); effects are handled by a per-effect-system bridge, ZIO first, cats-effect next, so a ZIO service layer drives the UI without the widget API knowing about F[_]. A Scala.js/HTML "dev canvas" backend gives the sub-second reload loop that makes Flutter and React Native popular.

The plan also weighs cheaper alternatives (Scala.js + React Native, Scala.js in a Tauri/Capacitor webview, ScalaFX + Gluon/GraalVM, sharing logic only) and states the go/no-go spikes that must pass before the ambitious path is committed to.

Documents

#	File	Contents
1	docs/01-vision-and-goals.md	Problem, vision, goals, non-goals, target platforms & priority
2	docs/02-what-makes-ui-frameworks-popular.md	Usability, platform fidelity, stability, performance — what the winners did
3	docs/03-landscape-and-alternatives.md	Survey of existing frameworks and of what Scala can reach today
4	docs/04-scala-toolchain-reality.md	JVM / Scala.js / Scala Native per platform: what works, what is unproven
5	docs/05-requirements.md	Functional & non-functional requirements (MoSCoW, numbered)
6	docs/06-architecture-options.md	Options A–F, trade-offs, scoring, recommendation
7	docs/07-technical-design-ideas.md	Core API sketch, reactivity, layout, renderer contract, threading, build, dev loop
8	docs/08-roadmap-and-spikes.md	Go/no-go spikes, milestones, exit criteria
9	docs/09-open-questions.md	Things we do not know yet and how to find out

Sources consulted are listed at the end of each document. Facts marked [unverified] are claims we could not confirm and that a spike must settle.