preCICE v2: A sustainable and user-friendly coupling library

preCICE is a free/open-source coupling library. It enables creating partitioned multi-physics simulations by gluing together separate software packages. This paper summarizes the development efforts in preCICE of past five years. During this time span, we have turned from working prototype -- sophisticated numerical methods and scalability on ten thousands compute cores to sustainable user-friendly project with steadily-growing community. Today, know through forum discussions, conferences, workshops, publications more than 100 research groups using preCICE. We cover fundamentals alongside performance accuracy analysis different data mapping methods. Afterwards, describe ready-to-use integration widely-used external simulation packages, tests, continuous unit system level, community building measures, drawing an overview current ecosystem.