File Extension RCX File Format Lego Mindstorms Robotics Invention System (The LEGO Group ) RCX stands for Lego Mindstorms Robotics Invention System (The LEGO Group ). This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question Printer plots to make its mark for Lego Creating not just consuming Take home a little bit of the LHC in LEGO!