This is an experimental tool for transferring files directly and securely between web browsers.
Why not? You don't need any cloud service for sharing a file. You can quickly share a file with anyone. File sharing is private; there are no file servers in the 'cloud'. Security; closing the browser tab will stop file sharing immediately.
It uses WebRTC (meant for video conferencing) technology to set up a peer-2-peer connection between browsers. The contents of the files are hosted on the server browser while the client browser pulls the file content directly from the server browser. This model is different than the traditional file sharing services where you first upload your files to cloud service and then the client pulls these files from the cloud provider. This entails trust in the cloud provider since it can, potentially, see your files.