Actually the question itself: how can you find out who is currently on the site at the moment and display its name? Required without using a database. While I am busy with sessions, but nothing comes out.
Common to all sessions of the site storage, most often - the database and file system. DB discard, remain files. You can organize in different ways.
In one file to write through the tab line:
userid timestamp имя
At each page request, read this file entirely, delete those lines where the timestamp is older than N, update it for the current user.
You can create in a separate folder for the file for each user , call them by id, or through the point id and name: "
15165.Вася Пупкин ". When prompted to update the contents of the file. And rely on the date of the file modification , to determine the time when people downloaded the page the last time. Files older than N erase.