Dew

Sandboxed desktop applets written in Luau and drawn by a native Rust renderer.

_{Dew's quick panel managing installed applets alongside running desktop widgets}

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Dew runs sandboxed desktop utilities called applets: clocks, hardware monitors, and HUDs. Each applet is authored in Luau, runs in an isolated guest environment, and renders using a native Rust rasteriser - no browser engine, Electron, or external runtimes required.

Applets construct their interface using declarative UI datamodel objects that are familiar to Luau developers (Frame, TextLabel, TextButton, UIListLayout, UDim2, Color3, etc.), implemented standalone, from scratch, in Rust, to run natively on desktop.

Featured Applets

System Monitor

examples/system/monitor/monitor.luau is a real-time hardware telemetry HUD showcasing dynamic visualizations and host telemetry gated by desktop.System.

id = "monitor"
name = "System Monitor"
description = "CPU, cores, memory, network, storage and top processes, live"

# Capabilities granted to the guest VM
permissions = ["widget", "storage", "system"]

• Live hardware telemetry: Monitors CPU utilization, memory pressure, network throughput, disk space, and top active processes.
• Dynamic visualizations: 60-second rolling CPU graph, 16 individual core bars, dual-channel network waveform, and memory consumption meters.
• Window management: Smooth dragging with display edge snapping (snapToEdges = true) and position persistence across restarts (savePosition = true).
• Capability-governed: Access to telemetry is strictly gated by the host under the system permission.

Desktop Clock

examples/clock/clock.luau is a minimalist, floating desktop clock widget demonstrating reactive UI updates and state persistence without external dependencies.

id = "clock"
name = "Desktop Clock"
description = "A minimalist, draggable desktop clock with live seconds and format toggle"

# Capabilities granted to the guest VM
permissions = ["widget", "storage"]

• Vertical gradient styling: Rounded widget with vertical gradient fill and outline styling (UIGradient, UICorner, UIStroke).
• Window management: Smooth dragging with display edge snapping (snapToEdges = true) and position persistence across restarts (savePosition = true).
• Interactive toggle: Click anywhere on the clock to toggle between 12-hour and 24-hour formats, saved across launches via desktop.Storage.
• Automatic timezone detection: Resolves local time and timezone offsets via desktop.Time.

Quick start

Requirements: a Rust toolchain (rust-toolchain.toml) and Rokit.

# Clone the repository
git clone https://github.com/dew-desktop/dew
cd dew

# Install pinned developer tools (lune, etc.)
rokit install

# Run the applets
cargo run examples/system/monitor
cargo run examples/clock

While running, Dew manages the widget lifecycle, handles window dragging and snapping, and sits quietly in the Windows system tray.

CLI Reference

Command	What it does
dew <path>	Run the applet in the specified directory
dew check <path>...	Validate manifests and entry points
dew snapshot <path> -o out.png	Render a single frame to PNG headlessly
dew snapshot <applet-id> -o out.png	Save the frame a running applet is showing, or render its installed copy if it is not running
dew test <path>	Run an applet's interaction tests
dew compat	Report which applets are portable across environments
--stats	Print a granular breakdown of layout and paint frame time
--bench	Force repaints every frame to measure continuous drag workload

Architecture

Crate	Responsibility
host	The dew binary: applet loader, manifests, capability injection, DataModel, layout, tray, and dashboard
crates/runtime	Embeds Luau through mlua. Rust owns the process; Luau executes as a guest
crates/raster	Translates display lists to pixels. CPU rasterization by default, GPU acceleration via feature flag
crates/window	Native window management, swapchains, system tray, and input events on Windows

Highlights

• Deny-by-default sandbox. Every applet runs in its own isolated Luau VM with no raw io, os, or FFI access. An applet can only reach capabilities explicitly granted in its manifest (e.g. storage, notifications, clipboard). The host injects each capability as a function, keeping security boundaries strictly auditable and testable in Rust.
• Engine-independent DataModel in Rust. The class hierarchy, properties, and defaults are driven by an engine reflection database, allowing the host to statically reject properties that do not exist on a class before values reach the layout pipeline. It covers 139 of 139 in-scope GUI properties.
• Native rendering pipeline. Layout, text shaping, strokes, gradients, clipping, and scrolling go through a high-performance CPU rasteriser built on vello_cpu, with an optional GPU backend via vello_hybrid and wgpu.
• Verified layout conformance. A shared conformance suite runs data-driven layout cases across implementations, asserting exact bounding boxes, text bounds, and flex allocations. A differential gallery validates that property mutations produce expected pixel changes.
• Fast frame budgets. Release builds render frames in approximately 1.7 ms. The built-in --stats flag profiles frame time across layout, shaping, and rasterization passes.
• Headless testability in CI. dew snapshot renders arbitrary applet frames directly to PNG without opening a window, allowing comprehensive integration tests to run in automated CI pipelines on Windows and Linux.

Development

cargo test --workspace                     # Rust unit and integration suites
lune run scripts/smoke.luau                # CLI validation checks
lune run scripts/verify_boundaries.luau    # Architecture boundary enforcement
cargo run --bin gallery-coverage           # Differential rendering coverage

CI builds on Windows, validates applet mounting, renders the gallery on Linux, and enforces formatting and clippy lints.

See CONTRIBUTING.md for workflow details. Contributions require signing the CLA.

Related Projects

• Aether: A headless Luau UI framework. Components run on Dew, across engine environments, and headlessly in CI.

License

Component	License
Client (host/, crates/)	PolyForm Shield 1.0.0: permitted for all uses except competing commercial products
Specification (docs/)	MIT, allowing third-party implementations to adopt the standard
Applets	Authored applets maintain their own licenses and never link against Dew

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_{Dew is an independent project and is not affiliated with or endorsed by Roblox Corporation. See NOTICE.}