API access to existing instance of a program

Hi there,

We have an application which our customer wants to be able to connect to using some kind of API. In the past we have done this using a TCP connection to recieve commands which works fine. In this case though, we are looking for a way to do it natively using C#.. is there a way to do this using remoting or something similar? Here's what we're trying to achieve:

1) User starts our client program (HClient)
2) The customer uses their program to access ours. I'm imagining some code similar to the following:

HClient hclient = HClient.GetInstance();
hclient.DoSomething();
hclient.DoSomethingElse();

I'm fine with creating an interface for the methods i want to expose, it's just the HClient.GetInstance() part im struggling with. I really want it to return a reference to the instance of HClient which is already running. Is this even possible? Im not sure where to begin researching.

Thanks for any help you can provide.