Ian Dunn

The <a href="https://wordpress.org/themes/p2" rel="ugc">P2</a> theme lets you quickly create posts from the front end, but by default it only allows you to tag them. This plugin lets adds a dropdown box to the post form so that you can also assign a category to the post.

P2 New Post Categories

Works nicely even on the "Mercury" child theme for P2 :)

Works!

Adds a dropdown menu of categories to the P2 new post form.

Thorsten Ott

Simple widget to extend P2s (and other themes) functionality and display recent @replies for a logged in user in the sidebar. 
It can be also configured to show direct replies to comments or posts without the @username indication.

Mention-Me Widget

11-year old plugin and it still works just fine! Sweet!

It works!

Simple widget to extend P2s (and other themes) functionality and display recent @replies for a logged in user in the sidebar.

P2 New Post Categories vs Mention-Me Widget