Last Post Date Column in the Users List
Shows when each user last published a post, which makes inactive authors easy to find.
Snippet Library
Users snippets for WordPress
Snippets for user accounts, roles and profiles: extra profile fields, new columns in the users list, last-login tracking and tighter control of what each role can do. Handy for membership sites, client sites and teams with many authors.
bbPress: Stop Replies to Old, Inactive Topics
Hides the reply form on topics with no activity for a set number of days and shows a note instead, which prevents necro-posting and old-thread spam.