[coffeeaddicted]

Ogre is a free open source library with a liberal MIT license unlike Unity or Unreal which are both proprietary tools. And in many projects you'll write your own editor so the lack of a good editor doesn't always matter. Being open source has a few advantages: You can adapt the engine to your project. You can learn how the engine really work. You can debug into the engine itself on troubles. You are less dependent on a company staying around maintaining a proprietary engine. You can influence the direction of development with patches.