The crux package for Emacs contains, amongst a list of useful functions (crux does stand for A Collection of Ridiculously Useful eXtensions for Emacs after all), the function crux-open-with. This interactive function opens the file you currently have open, or the file under your cursor in dired, using the system application for that file. On Ubuntu 16.04, this function unfortunately does not work. It looks like the application tries to start (icon visible in the dash) and then dies.
