June 21 - National Aboriginal Day in Canada. This date was chosen because it corresponds to the summer solstice, the longest day of the year, and because for generations, many Aboriginal groups have celebrated their culture and heritage at this time of year.
June 21, 1948 - The world's first stored-program electronic digital computer successfully executed its first program. That program was written by Tom Kilburn who, along with F.C. (Freddie) Williams, designed and built the machine. It was called the "Small Scale Experimental Machine", but was soon nicknamed the "Baby". [Source]
