Restad uses Qt and its qmake/project-file system.
Code documentation is generated by Doxygen, the config file is Doxyfile. Simply run doxygen in the project root dir and everything is created/updated in doc/html.
The project has some unit tests, see Tests.
If you want to contribute, you can check Todo List. The project uses Git. You can browse the code here https://sourceforge.net/p/restad/code/ . The classes of the project are grouped in subdirs, which are represented as modules in this doc, see Modules section. Here is a raw class diagram used as a draw for the project, not exhaustive, not up to date, not true UML but gives an overview of classes.
Class diagram