I dont know about a GNET-type server but you could just have an ascii file on some web space somewhere and as long as you have access to Perl you could use a cgi script to update it as soon as someone starts the app.
You just read the file to find out who's using it then.
There is a problem though... As soon as the app is started and tries to run your cgi script, their firewall will pop up. And if they dont let it out you won't get an accurate figure of how many people are using it.
[EDIT] Just figured a way to do it. If you launch Internet Explorer through the Execfile command (with the URL of the cgi script) this will get through peoples firewalls.
You just read the file to find out who's using it then.
There is a problem though... As soon as the app is started and tries to run your cgi script, their firewall will pop up. And if they dont let it out you won't get an accurate figure of how many people are using it.
[EDIT] Just figured a way to do it. If you launch Internet Explorer through the Execfile command (with the URL of the cgi script) this will get through peoples firewalls.