Downloading WorldEditor 1.5.0 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. This free software for Mac OS X is an intellectual property of Laminar Research. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The application lies within Games, more precisely Tools.
From the developer:
WorldEditor is an open source 2-d scenery and airport editor for X-Plane. Scenery in the X‑Plane simulator can include essentially everything outside the aircraft. X‑Plane is designed specifically to enable users to create and modify scenery themselves.
You may want to check out more Mac applications, such as Njam, rpgng or Petals Around The Rose, which might be similar to WorldEditor.