hi_class: Horndeski in the Cosmic Linear Anisotropy Solving System
  We present the public version of hi_class (www.hiclass-code.net), an extension of the Boltzmann code CLASS to a broad ensemble of modifications to general relativity. In particular, hi_class can calculate predictions for models based on Horndeski's theory, which is the most general scalar-tensor theory described by second-order equations of motion and encompasses any perfect-fluid dark energy, quintessence, Brans-Dicke, $f(R)$ and covariant Galileon models. hi_class has been thoroughly tested and can be readily used to understand the impact of alternative theories of gravity on linear structure formation as well as for cosmological parameter extraction. 
Miguel Zumalacarregui, Emilio Bellini, Ignacy Sawicki, Julien   Lesgourgues, Pedro G. Ferreira
astro-ph.CO gr-qc hep-ph hep-th