Unity is a fully-fledged game engine with a built-in drag and drop editor. Its main focus is 3D games, but you can also build 2D games with it, and lately there have been multiple improvements in this area.
Unity runs on Mac and Windows, and it has an experimental Linux editor that is not as stable as the others.
Unity’s recent versions only support 64bit versions of windows, so if you are running a 32bit version of the OS, you’ll have to pick up an older version.
