BuddyPress: Only Friends Can Send Private Messages
Limits BuddyPress private messages so members can only message people who have accepted their friend request, which cuts down unwanted messages.
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.
Limit How Many Users a Role Can Have
Caps the number of accounts for chosen roles, such as a maximum of 3 Editors, and blocks adding or promoting anyone beyond that limit.
Only Allow Registration From Certain Email Domains
Limits sign-ups to email addresses at the domains you list, for example your company or school domain.
bbPress: Limit New Topics per Member per Day
Caps how many new topics a member can start in 24 hours, which stops spammers and over-eager posters from flooding the forums.