D Cartwright

Included component allows group admins to easily promote/demote/ban members from all their groups.
It can be further extended using the standard buddypress profile subnav registration functions (for example, the bp-wiki plugin hooks into this to enable movement of wiki pages between groups).

BuddyPress Frontend Admin

This plugin brings site-wide-like administration options to the frontend, allowing group admins simpler management of all of their groups.

hardlyneutral

This plugin is built to display BuddyPress groups on the new user registration page. Groups can be displayed as:
<ul>
<li>a list of checkboxes</li>
<li>a list of checkboxes in a scrollable container</li>
<li>a list of radio buttons</li>
</ul>
New users will automatically join any of the groups selected during the registration process.
Options are available in the admin area to configure the title of the groups list on the registration page, the 
description of the groups list, whether private groups are visible to new users, the order in which groups are 
displayed, and how many groups will be visible.
<h3>Custom Styles</h3>
This plugin includes specific CSS for changing the way content is displayed. The default CSS will place the group after the “Profile Details” section and before the “Complete Sign Up” button on the register page. You can view <code>includes/styles.css</code> in this plugin directory to see how to target each element.
Here is a list of the current selectors used in <code>includes/styles.css</code>.
Groups section:
<pre><code>#registration-groups-section {
 float: right;
 width: 48%;
}
</code></pre>
Checkboxes:
<pre><code>.reg_groups_group_checkbox {
 margin: 0 5px 0 0;
}
</code></pre>
Form labels:
<pre><code>#buddypress .standard-form label.reg_groups_group_label,
.reg_groups_group_label {
 display: inline;
 font-weight: normal;
}
</code></pre>
Groups section – responsive:
<pre><code>@media only screen and (max-width: 480px) {
 #registration-groups-section {
 float: none;
 width: 100%;
 }
}
</code></pre>
List items:
<pre><code>.reg_groups_item {
 list-style: none;
}
</code></pre>
No groups message:
<pre><code>.reg_groups_none {
 font-style: italic;
 color: gray;
}
</code></pre>
Multiselect:
<pre><code>.reg_groups_list_multiselect {
 height: 8em;
 border: 1px solid #ccc;
 background: #fafafa;
 padding: 6px;
 overflow: auto;
}
</code></pre>

BuddyPress Registration Groups

Allows a new BuddyPress user to select groups to join during the registration process.

BuddyPress Frontend Admin vs BuddyPress Registration Groups