The Cocotron is hosted in a git repository on GitHub
You will need a git client on your machine, and can checkout the source with:git clone https://github.com/cjwl/cocotron.git
This will place the source in a directory named cocotron
The main project page is at:https://github.com/cjwl/cocotron
If you want to share your changes publicly, or just save them on GitHub, create a fork.