Another "unity-style" one to watch is Atomic Engine (https://atomicgameengine.com/ https://atomicgameengine.com/), which is from Josh Engebretson, who came out

Another "unity-style" one to watch is Atomic Engine (https://atomicgameengine.com/ https://atomicgameengine.com/), which is from Josh Engebretson, who came out of the GarageGames scene and is one of the most prolific and talented developers I've ever seen. Atomic is structured very similar to unity, has a C++ core and C# and Javascript bindings, but unlike unity the C++ core (as well as the editor) is open source so you can modify and customize it if needed.