Project Tox, also known as Tox, is a FOSS instant messaging application aimed to replace Skype.

With the rise of governmental monitoring programs, Tox aims to be an easy to use application that allows people to connect with friends and loved ones without the worry of privacy.

IRC: #tox on freenode, alternatively, you can use the webchat.
Website: http://tox.im

Website translations: see stal888's repository
Qt GUI: see nurupo's repository

How to build Tox on Linux: YouTube video
How to use Tox on Windows: YouTube video

The Complex Stuff:

• Tox must use UDP simply because you can't hole punch with TCP. It's possible, but it doesn't work all the time.
• Every peer is represented as a byte string (the public key of the peer [client id])
• We're using torrent-style DHT so that peers can find the IP of the other peers when they have their ID.
• Once the client has the IP of that peer, they start initiating a secure connection with each other. (See Crypto)
• When both peers are securely connect with the encryption, they can securely exchange messages, initiate a video chat, send files, etc.
  
• Current build status:

Roadmap:

• Get our DHT working perfectly.(Done, needs large scale testing though.)
• Reliable connection (See Lossless_UDP protocol) to other peers according to client id. (Done, see DHT_sendfiletest.c for an example)
• Encryption. (Done)
• Get a simple text only im client working perfectly. (This is where we are)
• Streaming media
• ???

For further information, check our To-do list

Important-stuff:

Use the same UDP socket for everything

Keep everything really simple.

Details and Documents:

DHT Protocol
Lossless UDP Protocol
Crypto
Ideas

Why are you doing this? There are already a bunch of free skype alternatives.

The goal of this project is to create a configuration-free p2p skype replacement. Configuration-free means that the user will simply have to open the program and without any account configuration will be capable of adding people to his friends list and start conversing with them. There are many so called skype replacements and all of them are either hard to configure for the normal user or suffer from being much too centralized.