LEAP (LivermorE AI Projector for Computed Tomography) is a C/C++/CUDA library of 3D tomographic projectors (forward and back projection) implemented for both multi-GPU and multi-core CPU. We provide bindings to PyTorch to achieve differentiable forward and backward projectors for AI/ML-driven computed tomography (CT) applications. LEAP contains more accurate projectors and FBP algorithms, more features, and most algorithms run faster than other popular CT reconstruction packages.