8 free tools for office & writing, 7 of them fully open source. Every one reviewed, with its licence and the paid apps it replaces.
Note-taking app with end-to-end encrypted sync

Office suite for documents, spreadsheets and slides

Markdown note-taking app built on local files

Outliner for linked notes and personal knowledge
Office editors with strong Microsoft Office compatibility
Reference manager for collecting and citing sources

Desktop publishing for print layouts and PDFs

Whiteboard for hand-drawn style diagrams and sketches