Quote Originally Posted by de_jean_7777 View Post
Unity3D leads in this area, and considering you can get it for free it's hard to compete with that.
You can start developing with Unity 3D for free but as soon as you sell enough copies of your software or earn certain amount of income you need to purchase the proffesional licence.
https://unity3d.com/company/legal/eula
So you can't actually say it is for free but it doesen't present you with initial expenses just to start developing with it as many other game engines do.