List of free docs stuff for developerππ½
If you're looking for all programming tools around docs (not just free). Check this page List of docs Programming Tools

Whimsical
Whimsical is the visual workspace for thinking and collaboration, combining flowcharts, wireframes, sticky notes, mind maps and docs. Crafted for speed and clarity.
Tag: docs, flowchart, mind map, wireframe, sticky note
Up to 3000 items per workspace Unlimited members Up to 10 guests per file or folder Real-time collaboration

Gitbook
GitBook helps you publish beautiful docs and centralize your teams' knowledge. From technical teams to the whole company.
Tag: knowledge-base, note-taking, docs
Unlimited Public Spaces Unlimited Private Spaces Advanced Editing Capabilities Publish And Customise Your Docs Custom Domains