The idea of BuddyPress is to take a standard vanilla installation of WordPress MU and turn it into something that represents more of a community building tool, or niche social network. BuddyPress is essentially a set of WordPress MU specific plugins. Each plugin adds a distinct feature (or component) to BuddyPress and only handles functionality for that specific component (for example, private messaging). The standard features of BuddyPress are:

Extended Profiles

The extended profile component allows site admins to create specific profile fields for their members to fill in. They can create as few or as many profile fields as they like, be as specific or vague as they want. Profile fields can then be grouped.

Personal Blog

This is everything WordPress has to offer for publishing a blog. The only difference is that all administration tabs will be moved underneath a “Blog” tab. A Member’s blog will also appear under “/membername/blog/” or /membername.domain.com/blog” rather than at the root.

Private Messaging

BuddyPress private messaging works like internal site email. Members can message people on their friends list as well as forward and reply to received messages.

Friends

Members of a BuddyPress social network can be connected together by one member adding another as a “friend” and then the other member accepting the friend request.

Groups

Groups in BuddyPress are a gathering of members, blog posts, photos and any other user generated content.

The Wire

This is a place where friends can come along and post to a members profile. This would be a short message and could include a picture and some basic HTML. The TinyMCE editor will be used to allow for basic formatting.

Status Updates

Status updates in BuddyPress will appear on a member’s profile page. A member can update their status as frequently as they want to. All status updates are logged in a member’s activity log.

Albums

Members of a BuddyPress installation will be able to create their own photo albums. These albums can be shared with friends and groups. Each member is given a certain amount of space, which can be set by the site administrator.

As each one is a separate plugin, there is no reason why site admins can’t pick and choose which components they want and don’t want. There is also no reason why additional components couldn’t be written, or other existing WordPress plugins be used alongside.

Pricing: Free
Source: http://buddypress.org