  Numerical simulations are ubiquitous in mathematics and computational
science. Several industrial and clinical applications entail modeling complex
multiphysics systems that evolve over a variety of spatial and temporal scales.
  This study introduces the design and capabilities of lifex, an open source
C++ library for high performance finite element simulations of multiphysics,
multiscale, and multidomain problems. lifex meets the emerging need for
versatile, efficient computational tools that are easily accessed by users and
developers. We showcase its flexibility and effectiveness on a number of
illustrative examples and advanced applications of use and demonstrate its
parallel performance up to thousands of cores.
