Butterfly is a free, open-source, cross-platform note-taking and drawing application built with Flutter and Dart, made for people who think visually and want an endless workspace for handwritten, typed, and imported content on desktop and Android.

What it is

Butterfly is a note-taking app that treats the page as an unlimited canvas instead of a fixed sheet. Notes, sketches, diagrams, images, and documents can be placed anywhere on the workspace, because the idea is to give messy, growing projects room to expand rather than forcing every thought into a top-to-bottom flow. It lives in the Flutter and Dart ecosystem, which is what lets a single codebase target Android and Linux alongside other platforms, and it is developed in the open by Linwood under the AGPL-3.0 licence.

The concrete thing it replaces is the fixed-page, linear text editor. The README states the contrast directly: instead of writing everything from top to bottom on a fixed page, users get an endless workspace where they arrange material spatially. It also replaces the split workflow of drawing in one tool and writing in another, since handwriting, typed text, Markdown, shapes, images, photos, PDFs, and SVGs all sit on the same canvas. Work moves in through imports and out through exports, so the canvas acts as a workspace rather than a locked-in silo.

Key capabilities

• Tunable drawing tools, with per-pen control over smoothing, thinning, pressure behavior, zoom-dependent strokes, and shape detection.
• Mixed content on one canvas: handwriting, text, Markdown, shapes, images, photos, PDFs, SVGs, rulers, grids, and textures.
• Presentation support, including presentation tools and laser pointer notes for walking an audience through a canvas.
• Import of PDFs, SVGs, and image files, so existing reference material lands directly in the workspace.
• Export to PDF, SVG, images, or portable Butterfly files, which keeps the work movable rather than trapped in a proprietary format.
• Cross-platform builds, with Android and Linux named among the supported targets.
• Customizable behaviour, listed as a first-class topic alongside drawing itself.

Who uses it and how

• Students and teachers taking class notes, working through math, or building worksheets on a canvas that tolerates revision.
• Meeting and research note-takers who need to mix typed remarks with quick sketches and pasted references in one place.
• Planners and whiteboarders running brainstorming, storyboarding, or product sketch sessions where the structure only emerges over time.
• Handwriters and typists working side by side, since input comes from a stylus, touch, or a mouse and can be combined with typed Markdown.
• Android and Linux users who want the same workspace on both, rather than one platform's app and another's compromise.

Getting started

Downloads are published on the official site at https://butterfly.linwood.dev/downloads, with released builds also listed on the project's GitHub releases page. The repository is written in Dart, so building from source requires a Flutter toolchain.

How it compares

No paid products that Butterfly replaces are listed in the facts, and no similar tools are named either. On the evidence available it stands alone in this registry: an AGPL-3.0, cross-platform drawing and note-taking canvas with no named counterpart.

When to use it — and when not to

Choose Butterfly if an endless canvas, stylus input, and mixed handwriting-plus-Markdown content match how you work, and if an AGPL-3.0 licence suits your use. Be aware that the licence is copyleft, which matters if you intend to build on the code in a closed product, and that the README excerpt available here is sparse on installation and deployment detail beyond the downloads page. It is a client application rather than a hosted service, so anyone expecting a server component, account system, or sync backend will not find one described in the facts.