[ivantung]

You don't need anything fancy here. Coming from the game industry where frame updates are typically targeted at 60 Hz or 16.66 ms per frame. Even mobile games often target 60Hz. During the 16ms a game typically has to do a lot of stuff such as ai, rendering, user input. So in comparison your needs are very light. You can probably develop what you need in any number of languages and OS. I would go with what is you are comfortable with. Take a look at SDL2, you could probably put together something in one day. The only thing unusual you mentioned is the external triggering mechanism. Whatever this is you will need some kind of device API/interfacing code, so this may decide which OS you will need to use. SDL2 is cross platform so you should be good to go there.