This creates links to page showing all other pages sharing the tag. See the documentation for other uses.
Additional tags could reflect the topic of the idea, it's geography (city or canton), etc. For example, the Open Budget of Bern project should use the 'finance bern dataviz' tags so we can quickly jump to related projects.
With this we can now list projects by their status (e.g. concept, mockup, live), and create a page showing all projects by topic (e.g. transport, health) or projects that needs:dev or has:data.
We have yet to go through and tag each existing project, but we'll start using this system at the next hackdays.