Actual first step workout was at the gym in the early 80s. Complex routines were my favourite, designed by the instructor. Then the gym introduced Les Mills, which was nowhere near as much fun, just the music was better.
First home step workout was
Cory Everson's Step In Time in 1998
My 'step' was the children's alphabet puzzle mats joined 3-in-a-row & stacked, then broad cotton tape wrapped around, catching on the puzzle knobs to hold it together. DH scoffed with "How long with this last?"
He bought me a Reebok step for Christmas 6 months later.