Scriblio enables faceted searching and browsing of WordPress posts, pages, and custom post types. Tags and other taxonomies are represented as clickable facets that you can use to explore a site.
The facets widget makes it easy to explore your blog using tags and other taxonomies attached to your posts. Tag clouds are calculated based on the posts in each found set. Clicking a tag adjusts the search to show the posts matching all the selected tags and again recalculates the tag cloud. (Facets can be displayed as either tag clouds or lists.)
The search editor widget shows all the selected search terms (including keyword searches, tags, and other taxonomies) and allows the user to remove terms from the search or click any of the displayed terms to search only that item.
Scriblio includes live search suggestions that recommend search terms based on the tags (and all public taxonomies) and post titles.
In the WordPress.org plugin repo
This plugin is on Github: https://github.com/misterbisson/scriblio