All the source-code is available on Github. It is well documented so do not hesitate to read the README files. Pull-requests for features or bug-fix are really appreciated !
To reach the development team, write to the developers mailing-list at firstname.lastname@example.org.
You may also register to that mailing-list by sending an empty email to email@example.com. If you intend to become a regular freelan developer, registering is mandatory.
The latest protocol specification is always available here. Feel free to make suggestions or improvements if you notice that something is suboptimal.