What are some alternatives?
When comparing RetroX and Retropie, you can also consider the following products
RetroArch - RetroArch is a frontend for emulators, game engines and media players.
LaunchBox - LaunchBox is a portable, box-art-based games database and launcher for DOSBox, emulators, arcade cabinets, and PC Games. Download it free!
MESS - Emulates most gaming systems that exist, emphasizing accuracy over speed.
Lakka - Lakka is the official Linux distribution of RetroArch and the libretro ecosystem.
higan - higan was formerly known as bsnes. The project was renamed after becoming a multi-system emulator.
Mame - MAME stands for Multiple Arcade Machine Emulator.