The best open source alternative to Notion is Standard Notes, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 100 alternatives to Notion and loads of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Notion are CherryTree (Free, Open Source), Zim (Free, Open Source), TiddlyWiki (Free, Open Source) and Zettlr (Free, Open Source).
Zettlr is a supercharged markdown editor that combines many writing editor features and collect them in one application. It aims at speeding up your workflow and help you write without any interruptions.
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, including this website, the home of MediaWiki.
This is a ToDo List / Time Tracker / Personal Jira Task Manager for Linux, MacOS and Windows to make you work super productively. * Plan, track & summarize. Create time sheets and work summaries in a breeze to easily export them to your companies time tracking system.