Dennis Ploetner

Display a recent posts-widget of all your posts in your blog-network which have a specific tag, category or any other built-in or custom taxonomy.

Multisite Taxonomy Widget

List the latest posts of a specific taxonomy from your blog-network.

Prasanna SP

This plugin creates a new widget which allows you to show recent posts by tags. The default Recent Posts widget in WordPress shows recent posts belonging to all categories. But this plugin gives you the option to show recent posts by tags. It is helpful if you are mainly using tags to categorize your posts.
Visit developer’s blog at <a href="http://www.prasannasp.net/" rel="nofollow ugc">prasannasp.net</a>
Support: Please post your support questions at <a href="http://forum.prasannasp.net/forum/plugin-support/wordpress-recent-posts-by-tags/" rel="nofollow ugc">Recent Posts by Tags plugin support forum</a>
Visit <a href="http://www.prasannasp.net/wordpress-plugins/" rel="nofollow ugc">this page</a> for more WordPress Plugins from the developer.

Multisite Taxonomy Widget vs Recent Posts by Tags