We describe a user-friendly open-source cross-platform radiative transfer application called bytran targeting mobile devices we developed using Qt/C ++ for the calculation of molecular and atmospheric absorption of gases under user-defined meteorological conditions and for specified gas mixture concentrations. Bytran is based in part on the HITRAN Application Programming Interface (HAPI) source code and relies on data provided in the online version of the High-Resolution Transmission Molecular Absorption Database (HITRAN) for line-by-line calculations. The novelty of the implementation is the usage of the recently introduced HITRANonline database (HITRAN.org), native execution of the line-by-line calculations on portable electronics hardware, and the cross-platform open-source implementation which also allows compilation of the bytran source code for desktop operating systems and embedded development boards. The application has the potential of becoming useful for in-the-field scientific evaluations as well as an educational tool for students studying spectroscopy and related subjects. Additional availability of the application under desktop environments further expands the possible usability of the developed software for in-the-lab settings. Ongoing work includes optional usage of pressure, temperature and humidity sensors available in selected cell phone models and the Raspberry Pi Sense Hat add-on board to generate spectra based on detected ambient meteorological conditions.