What it does

NebulaTransfer moves files directly between two devices over an encrypted WebRTC connection. The file never touches a server: a small signalling server only introduces the two browsers, then gets out of the way.

Any device with a browser. Phone to laptop, Windows to Mac, Android to Linux. Nothing to install.
Big files. Up to 100 GB per file. Received chunks go to browser storage as they arrive, so memory use stays low.
Private by default. The data channel is encrypted (DTLS). An optional 6-digit PIN makes sure the right person is accepting.
Several files at once. Drag and drop, browse, or paste; files are queued and sent one after another with live speed and time remaining on both ends.

How to use it

Open the app on both devices. Each one gets a short ID such as k3x9-qp7m and a friendly name such as Peachy Koala.
Link them. Type one device’s ID into the other, open its share link, or scan its QR code with a phone camera.
Send. Pick the device, drop your files in, and press Send. Switch on Protect with PIN and read the code out to the other person.
Accept and save. The receiver accepts (typing the PIN if asked), watches the progress, then previews or saves the file.

Keep both tabs open until the transfer finishes. If a network blocks direct connections, the transfer is relayed through an encrypted TURN server instead.

How it works

Two browsers exchange connection details through PeerJS, open a WebRTC data channel, and run a small protocol on top: an offer the receiver must accept, a PIN check, 256 KB chunks with a sliding window of eight unacknowledged chunks, and a final confirmation that every part arrived. The full story, with diagrams, is in the blog post.