Sorry about that. It’s morning here in Seattle, and I have only had one cup of coffee. A poor excuse, but an excuse nevertheless.
Option 1
{{ $p := slice }}
{{ range site.Taxonomies.tags }}
{{ range .Pages }}
{{ $p = $p | append . }}
{{ end }}
{{ end }}
{{ range uniq $p }}
<h2><a href="{{ .RelPermalink }}">{{ .Title }}</a></h2>
{{ end }}
Option 2
{{ range where site.Pages "Params.tags" "ne" nil }}
<h2><a href="{{ .RelPermalink }}">{{ .Title }}</a></h2>
{{ end }}
The only limitation with the second approach is that it will include pages with an empty tag array:
tags = []