Wikipedia
TressFX
AMD TressFX is software library which provides for advanced simulation and rendering of hair, fur, and grass to be processed by the GPU. The initial library was written to perform well on AMD's GCN-based products. Version 3 as released on January 26, 2016, worked solely with for Direct3D 11 and utilized DirectCompute.
A competing solution offered by Nvidia is HairWorks which is part of their Nvidia GameWorks suite, and is proprietary in nature.
Released as part of GPUOpen AMD TressFX is free and open-source software subject to the MIT License.