Fandem is a Peer to Peer (P2P) file transfer app, meaning that the data sent goes directly to the other device, without any intermediate server in between. This kind of transfer allows you to keep your data private, since only the two devices making the transfer will access your data.
The transfers are performed using your Wi-Fi (or smartphone's data), so they are a lot more faster than with bluetooth!
Fandem android is part of the following open-source project