Thinking Worlds, from Caspian Learning, is an authoring platform for virtual worlds highly focused on creating structured learning experiences. No advanced programming experience is required as wizards are provided for most development. Additionally it integrates with existing e-learning platforms (LMS) by outputting SCORM compliant modules.
Games developed with Thinking Worlds can be played in standalone, in-browser (using a Java or Shockwave plugin) or in iOS. A free version of this engine is available, check out its demos.
Kineo review of the platform: https://www.kineo.com/authoring-tools/caspian-thinking-worlds.html.