Java applet for OS X 10.9 (Mavericks)
To open the app right-click it and click 'open'. This will open the app with Apple's Gatekeeper (System Preferences > Security &amp; Privacy > General) still activated.

You can see more about this on Apple.com (WWDC video) and on Apple's Developer pages.

Other URLs:


About Gatekeeper



  Mac App Store and identified developers (default in OS X Mountain
  Lion) – Only allow apps that came from the Mac App Store and
  developers using Gatekeeper can open.



macOS Security



  Gatekeeper gives you two security options. The default option allows
  you to download apps from the Mac App Store, as well as those from
  other sources that are signed with an Apple ID.



macOS Human Interface Guidelines: Gatekeeper



  Users can set Gatekeeper to download and install:
  
  (...)
  
  Apps from the Mac App Store and apps signed with a Developer ID (this
  is the default setting) With the default setting, if an app is
  unsigned, Gatekeeper blocks the app from installing and warns users
  that the app did not come from an identified developer. Users can
  choose to override Gatekeeper or change the settings.