Re: How to retrieve online connected users in applications
Your question is so vague that it makes it essentially unanswerable. If clients are connecting via sockets, you keep track of open sockets and query the RemoteEndPoint property (link) of each open socket. If you're talking about something else, you'll have to be more specific to get a reasonable answer out of the forum.
All advice is offered in good faith only. You are ultimately responsible for effects of your programs and the integrity of the machines they run on.