GoodNotes is not available for Linux but there are plenty of alternatives that runs on Linux with similar functionality. The best Linux alternative is Obsidian, which is free. If that doesn't suit you, our users have ranked more than 50 alternatives to GoodNotes and 16 are available for Linux so hopefully you can find a suitable replacement. Other interesting Linux alternatives to GoodNotes are Xournal++, xournal, OpenBoard Whiteboard and Linwood Butterfly.
Notetaking and blackboard replacement application. Inspired by Xournal. Written in C++/Qt for Linux / Windows. It has the ability to annotate PDF files and has a few other options (e.g. markdown support).
Notetaking and blackboard replacement application. Inspired by Xournal. Written in C++/Qt for Linux / Windows / Mac.
Rhyolite is a simple markdown editor build using tauri framework that allows user to edit and work on markdown files.
Gournal is a note-taking application written for usage on Tablet-PCs (such as the Toshiba M200)
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Though it is not available on iOS, this application supports handwritten notetaking as well as PDF annotation. This makes it an alternative based on featureset.