Vlinder is an app that makes your device part of a network through which a butterfly can fly. There is only one butterfly and it can only be at one device at a time.
When the butterfly flies to your device you'll receive a notification and be able to see the Vlinder. It will then fly to the next closest connected device, ad infinitum.
Check the Vlinder Facebook page for screenshots where it has been: https://www.facebook.com/Vlinder-874856842537755/ and feel welcome to post your captures there too.
To see where Vlinder is right now visit http://www.vlinder.co/map