alsultaneo/2cup

2cup Chat is a peer-to-peer chat application for Windows, built in Go with a deliberately retro Windows 95 style interface. There is no central server involved. Instead, the app finds other users directly over the internet using a shared peer discovery network, connecting straight to them when possible and falling back to relay methods when firewalls or restrictive networks get in the way. Every message is encrypted before it ever leaves your computer. The app offers two ways to chat. Join Chat lets you create or enter a room using a six digit code plus a password, and anyone with both can decrypt that room's messages, images, and voice notes. Messages mode is for one-to-one conversations: you register a local account with an email and password, which are stored only on your own device, and you get a permanent numeric ID plus a public and private key pair. You add friends by their ID and exchange encrypted text, photos, voice notes, and files, with delivery attempted directly first, then through a broader broadcast method, and finally through a store-and-forward relay if your friend is offline. Peer discovery and getting through difficult home network setups happen automatically using a distributed hash table and related peer-to-peer networking techniques, and any user whose connection is reachable from the internet can automatically help relay traffic for others stuck behind more restrictive routers. The app includes a built-in connection test screen that checks each part of the networking stack and explains likely causes when something is not working, such as a firewall blocking traffic. To run it, you need Windows 10 or 11, and building from source requires Go version 1.21 or newer with no separate C compiler needed. The project is upfront that it has not had a formal security audit and suggests using it for casual conversations rather than anything sensitive, since anyone who knows a room's code and password can decrypt that room's traffic. The project is released under the MIT license, so it can be used, modified, and shared freely.