Joplin

Joplin is a free, open-source note-taking app that uses Markdown and offers end-to-end encrypted sync via various cloud services. It includes a web clipper, notebook organization, and strong search. Data is stored in portable formats. It's perfect for users prioritizing open-source software, strong encryption, and avoiding vendor lock-in.

It's completely free. It scores for its reliability, strong privacy features, and flexibility in syncing, making it a trusted choice for secure, cross-platform personal knowledge management.