Hello y'all! I'm new here. Found my way via google, while trying to find an answer to my question.
I am currently working on a horror game. The story, concept art, level design and a few 3D models are all completed (but are most likely subject to change later on).
The build of the game I am working on is only for promotional use to get funding, for example, a free to download demo on a funding website like Kickstarter.
Now I'm looking for an engine to work with after finishing the demo.
These are the engines (that I can remember from the top off my head) that I am familiar with: Source, Unreal Engine 3, CryEngine 1-through-3 and have lately been trying out the HPL2 engine (designed for the horror genre, after all). I am currently working in UE3.
Question: What engine would be legal to use? I plan on selling the game, and I am looking for an engine, hopefully similar to the ones listed above, that would be legal to use.