Recently Unity announced a pricing update which changes the pricing model from a simple pay per seat to a model whereby developers have to pay per install. This isn't restricted to paid installs or plays; it applies to every plain install.
This price change has some particularly grave consequence
What open source engines are there? No open source engine will have as much resources dedicated to it as unreal or frostbite for example.
Godot is probably the most well known open source engine