RiftShare does not collect or store any personal information about you. However, RiftShare is a file transferring tool. Your files will either be sent via the local network, or via the internet. When you transfer files on the local network, traffic should stay on the local network after negotiating a connection. When transferring files through the internet, a tcp relay server is used if a direct connection cannot be established. The tcp relay does not have access to any of the transferred data as it is encrypted.
In order to facilitate the file transfers (discoverability and private key exchange), a connection to the magic wormhole servers is necessary. Please read more about this process here.
You are free to validate any of these claims as the source code for this application is freely available.