Rotorcross in an open source multirotor racing simulator. You can contribute to it at https://github.com/sramzel/Rotorcross. For my RcGroups friends: http://www.rcgroups.com/forums/showthread.php?t=2613614#post34122552.

Features:

• Real life physics running at 285 frames per second
• 4 PID controllers from CleanFlight
• Customize your multirotor
  • PID settings
  • Motor specs
  • Propeller dimensions
  • Frame size
  • Battery voltage
  • Camera and OSD
• Adjustable AI
• 4 levels
• 6 timed courses

Note: For Mac OSX Yosemite, you have to run this terminal command to get it to work:

chmod +x /PATH/TO/APP/contents/macos/*

Thanks TheKLaMike!

Note: For Linux blackscreen issue, 'beautiful' and 'fantastic' settings do not work, try 'good'.

Thanks ohmyfsm!