Custom VNC type remote desktop client/server

I have a number of computers in remote locations and am currently using VNC/teamviewer to control these computers. Each computer has approximately 1 dozen windows applications running, each of which I need to control at random times. What I would like is a software solution, that detects when a window from one of the remote computers requires attention (it flashes) and immediately transmits this window only to my main computer, allowing me to control it remotely. The software will allow for multiple occurances of different windows from the same computer, as well as multiple windows from multiple computers There should be no limit to the amount of client computers I can use, or the amount of concurrent windows that I can remotely control from one or all clients. I expect this to be a server/client type application.