I was thinking more of a pc app or raspberry app. anything that echo could talk to via the internet.
Echo can't talk to your PC/Raspberry/Mac/etc via the internet, at least not directly, nor is there any native Alexa support for such communication. What Alexa
can do on behalf of your Echo is invoke a user-written "skill" that could forward the text of a command to an app running on one of those platforms. But you would need both components working in conjunction with one another, not just an app running on the target platform. Maybe there's an IFTTT recipe for something like that, but I've never seen one.