Re: So WebGL
It's non-proprietary and doesn't require a licence for any sort of deployment.
It's also a completely different product. WebGL is a thin hardware abstraction. Think of it like assembly language. You directly control the primitives to be drawn and the function applied to determine the colour of each pixel of each primitive.
Unity is a game-engine. Think of it more like the combination of C# and the Windows Presentation Foundation. You describe a number of objects within a scene and their properties. So it's a much higher-level thing that technically constrains you to certain semantics but which is designed to be broad enough for a huge proportion of use cases. It will be using WebGL to render.