>This is something that I don't know. It could be up to 20 people who will simultaneously be using the application. How *active*, I don't know.
>But do I understand correctly that it would be like running 20 copies of my VFP application on my PC?

People do that all the time. I guess they use the same guidelines.

>Another *unknow* for me is the following. On a PC/notebook, the application can be loaded only once. That is, I use some old code that checks if the application already runs and does not start it again.
>I am confused then as to how it will run on the Citrix server. If user 1 starts the application, does it mean that user 2 will use the same instance of the application, under the same credentials as user 1?

Now it depends on how they log in... if everyone has one's own login, they run in separate memory spaces and your mutex checker shouldn't find another instance. If several of them use the same login, then I don't know. But they may use the same temp folder (there's one per login, probably whole %appdata% space per login) and that's where you may have trouble if they happen to create files with identical names.