PyCOOL (Cosmological Object-Oriented Lattice code) is a fast GPU accelerated program that solves the evolution of interacting scalar fields in an expanding universe with symplectic algorithms. The program has been written with the intention to hit a sweet spot of speed, accuracy and user friendliness. This is achieved by using the Python language with the  PyCUDA interface to make a program that is very easy to adapt to different scalar field models.  The program is publicly available under GNU General Public License at. See the PyCOOL website for more information.