LB Users Counter is a plugin for WordPress. Allows you to add a widget to a sidebar, where you can view some attributes with respect to the number of users browsing the website (online, offline and online user name).
API Reference
User Class
This class contains the static methods for get info of users login
User::getUserOff() This function get number of users offline.
User::getUserOn() This function get number of users online.
User::getNameUserOn() This function get the names of users online.