We use will to make predictions about the future based on what we think or imagine or for on-the-spot decisions. I think life will be very different in 2100. It's too hot. I'll open the window.
We use be going to to talk about future plans & intentions or to make predictions about the future based on what we see. He's going to buy a new car. Look out! You're going to fall.
We use the present continuous to talk about fixed arrangement in the near future. I'm seeing Amy tonight.