This hook can be used to add a addtional widget on group sidebar. Example https://www.opensource-socialnetwork.org/component/view/3305/group-invitation

<?php
function my_component_init(){
		ossn_add_hook('group', 'widgets', 'my_component_hook');
}
function my_component_hook($hook, $type, $widgets, $params){
		//$params['group'] contain OssnGroup instance.
		$widgets[] = 'new widget contents';
		return $widgets;
}
ossn_register_callback('ossn', 'init', 'my_component_init');