For example, TradeIdeas has a feature in their stock screener software called "external linking" that allows you to link a text box from an external application (like your stock broker's software) to the TradeIdeas software. Then when you select a stock ticker from the TradeIdeas application window, it will then automatically input that stock ticker into whatever externally linked application window you configured. I don't know what language TradeIdeas is written in unfortunately. I would like to replicate this behavior in my own custom application.
If anyone can point me to an API I would greatly appreciate it!