At some point, after bicycles became a major mode of transportation, the progression within part of the industry was directed at smaller and more personal modes of transportation. One of the earliest examples were the Ritter Road Skates 1898 which completely powered by the user. Over the next quarter-century, various inventors attempted to motorize such roller skates
"Motorized," in this context, doesn't necessarily mean that a traditional gas motor was attached to the skates. However, there were several gas powered skates made. There were also electrically powered skates made, too. For those folks that may have been worried about a combustion engine exploding underneath their feet, or getting electrified, or being exposed to the exhaust and noise, there were skates proposed for these users, too. Such roller skates captured the downward pressure of the user by utilizing racks-and-pinions, gears, springs, cam shafts or any other similar mechanical option to propel them forward.
Some examples of these motorized roller skates were actually really basic. Take for example the set of skates with bicycle-size wheels attached to the leg, or the pair that looked like a common pair of skates but with 9 wheels each.