CoApp is currently undergoing a bit of a cleanup on GitHub.
This is the "core" project. There is a solution in here which can be built without the Windows SDK/DDK but following the instructions in https://github.com/coapp/coapp.org/wiki/Setting-Up-Your-CoApp-Development-Environment is still recommended.
If anything doesn't make sense or documentation looks incomplete - log an issue https://github.com/coapp/coapp.org/issues.
Once you've cloned the repository (git clone firstname.lastname@example.org:coapp/coapp.git) you should be able to build it from the command line using
pTk (included in a submodule):
cd coapp tools\ext\ptk build release
or open one of the
.SLN files in Visual Studio:
coapp.sln -- contains the projects without the tricky-to-build prerequisites (native dlls and bootstrappers)
coapp-with-prerequisites.sln -- contains the projects with the tricky-to-build prerequisites (native dlls and bootstrappers)
It is not recommended that you use this project, the prerequisite DLLs must be digitally signed to work correctly (which is why the signed copies are shipped in the ext/binaries submodule)