Joplin is an open-source clone of Microsoft OneNote. It's a stand-alone software client and not a service. However, it has built-in support for syncing with any WebDAV-capable server, Microsoft OneDrive, or DropBox. It has optional support for end-to-end encrypted notes. The Linux, macOS, and Windows desktop apps are a bit slow but they get the job done. They don't stand out from the competition in either a positive or negative way. The Joplin app for Android is another story entirely.