TREX is a highly integrated initiative that gathers most European leading scientists in quantum mechanical simulations of extreme accuracy in the framework of stochastic quantum Monte Carlo methods. This methodology represents one of the highest steps in precision in the ladder of electronic structure approaches and is uniquely positioned to fully exploit the massive parallelism of the upcoming exascale architectures. The marriage of this sophisticated approaches with exascale computing is bound to enable molecular simulations of unprecedented accuracy for complex scientific and industrial applications, meeting the growing demands for robust and predictive calculations in materials design. Thanks to co-design activities with leading high-performance computing (HPC) stakeholders, TREX will deliver a sophisticated product consisting of a user-friendly, high-performance software platform in the domain of stochastic quantum chemical simulations, which will enable the convergence of HPC and high throughput computing (HTC), and which will be made fully available to the computational community in academia and industry. Finally, TREX will work on show-cases to leverage quantum Monte Carlo methods for commercial applications as well as develop and implement software components and services that make it easier for commercial operators and user communities to use HPC resources for these applications.