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Free, open-source note-taking with rich text, cross-platform support, syntax highlighting, embedded files, and customizable interface.

Whether it's bookmarks or passwords, files or shopping lists...Turtl organizes it all and makes it easy to find later. Sync across your devices. Leave nothing behind.

neutriNote is an all-in-one preservation of written thoughts, be those text, math (LaTeX), rich markdown, drawings, etc., in fully searchable plain text (universal UTF-8).

Markdown is a text-to-HTML conversion tool for web writers. Markdown allows you to write using an easy-to-read, easy-to-write plain text format, then convert it to structurally valid XHTML (or HTML).

Made by the company behind WordPress, Simplenote enables users to take notes, lists, and ideas. These notes are stored on the cloud and are accessible across multiple devices.

Open source note-taking app with Markdown support, to-do integration, and synchronization with cloud services like Dropbox and OneDrive.

Plain text notepad with markdown support and todo list manager for Linux, Mac OS X and Windows, that works together with the notes application of ownCloud.

wikidPad is a Wiki-like notebook for storing your thoughts, ideas, todo lists, contacts, or anything else you can think of to write down. What makes wikidPad different from other notepad applications is the ease with which you can cross-link your information.

TiddlyWiki is a single html file with all the characteristics of a wiki - including all of the functionality (including editing, saving, tagging and searching) and the style sheet. Because its a single file, its very portable - you can email it, put it on a web server or share...

MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia. It is now used by several other projects of the non-profit Wikimedia Foundation and by many other wikis.

End-to-end encrypted note-taking with offline access, unlimited sync across devices, tagging, passcode and biometric security, plus advanced premium privacy features.

OpenSource note-taking & archiving alternative to Evernote, Microsoft OneNote & Google Keep.

Laverna is a JavaScript note taking application with Markdown editor and encryption support. Consider it like open source alternative to Evernote.

A cross-platform Markdown editor providing real-time preview, Focus & Typewriter modes, and support for multiple export formats.

Leanote provides services for note and blog. You can use "note" as your personal notebook, if you want to share with friends, just publish note or notebook to the blog.