Open-source GoodNotes alternative

Butterfly is an open-source app for people who think better with space around their ideas. Instead of a fixed page, you get an endless workspace where notes, sketches, diagrams, images, and documents can be placed wherever they make sense. It is built with Flutter and released under the AGPL-3.0 license.

You can write by hand with a stylus, touch, or mouse, type text with Markdown, and mix in diagrams and imported documents. The README suggests uses such as class notes, meeting notes, research, math, worksheets, planning, whiteboarding, storyboards, and product sketches. Topics list Android, Linux, Windows, and web builds, and describe it as customizable and a OneNote alternative.

The project is run by Linwood and invites translations through Crowdin, with community spaces on Matrix, Discord, Mastodon, and Bluesky. It suits students, teachers, and visual thinkers who want a flexible digital notebook that keeps their canvas under their own control.