https://www-ljk.imag.fr/membres/Pierre.Saramito/rheolef Rheolef is both a C++ library and a set of commands for unix shell programming. Rheolef expressions bases on the variational formulation of PDEs: polynomial spaces, fields and bilinear forms are C++ types for variables, that can be combined in any expressions, as you write it on the paper.
Combined together, as a Lego game, these bricks allow the user to solve most complex nonlinear problems. The Book details, step by step, how some simple and more complex problems can be solved, most of them in less than 20 lines of code. The concision and readability of codes written with Rheolef is certainly a major keypoint of this environment.