You will notice a link to the source code on the left. Monal is available under the BSD licence. It is hosted with Assembla at the moment and I am going to move it to github soon so that I can take pull requests easier.
There is a lot of very very old code from 2008 in the app still that I haven’t had time to rewrite — you will notice it when you see it. I am also in the process of some major overhauls so I am not sure how good of a learning tool it is at the moment. In any case, feel free to browse the code.