HackADay is described as 'Hackaday.io is a platform for people who like to build things'. There are five alternatives to HackADay for various platforms. The best alternative is Wikifab, which is both free and Open Source.
The list of alternatives was last updated Nov 25, 2020
Wikifab is a wiki-based site. The platform documents instructions for simple and technical projects. You can create new tutorials for projects or make edits to current projects to enhance them. View 3 alternatives to Wikifab