AppFlowy

AppFlowy is an open-source alternative to Notion, offering a similar block-based editor, databases, and Kanban boards. You can self-host it for full data control or use their cloud. It emphasizes privacy, customization, and community-driven development. It's ideal for Notion users who want open-source software, more control, or the ability to modify the tool.

It's free to use. It scores for providing a viable, community-backed open-source option with a familiar interface, appealing to tech-savvy users and organizations with strict data policies.