  This paper presents the basic concepts and the module structure of the
Distributed and Unified Numerics Environment and reflects on recent
developments and general changes that happened since the release of the first
Dune version in 2007 and the main papers describing that state [1, 2]. This
discussion is accompanied with a description of various advanced features, such
as coupling of domains and cut cells, grid modifications such as adaptation and
moving domains, high order discretizations and node level performance,
non-smooth multigrid methods, and multiscale methods. A brief discussion on
current and future development directions of the framework concludes the paper.
