The latest release of P3DFFT++ can be downloaded here.
To install, modify the makefile to set C++ MPI-enabled compiler appropriate to your system. Also edit the location of FFTW or MKL libraries. Several site-specific makefiles are provided as examples. make lib will build the library.
In addition, if you wish to build example programs in C++, C and/or Fortran, follow the same steps for makefile in each of the subdirectories. Then type make samples in the top directory to build all 3 language examples. make all or make builds both library and examples.