RetroArch's Steam release has been delayed to later this year
Originally planned for a launch at the end of this month, Libretro has announced that they will be postponing the release of RetroArch for Steam. The reasoning behind the delay is that the team wishes to have a more polished version that, "will meet the user expectations of your average Steam user". RetroArch will now launch sometime soon, in the third quarter of 2019. Regardless of the Steam version's delay, the latest RetroArch update, 1.7.8, will not be affected, and is still slated to be out within the next two weeks.
and pulled from there website as a free download for all platforms that have steam, RetroArch only Available on Steam!!