What the heck is a Micromoteur? A small engine fitted to a bicycle to power it along. I suppose for going up hill.

https://roweryzsilnikami.wordpress.com/1922-labinal-micromoteur/

https://roweryzsilnikami.wordpress.com/1923-austro-motorette/

https://roweryzsilnikami.wordpress.com/1924-sheppee-cykelaid/

And then there is this frame mounted JES from 1910... and it looks like a marvelous smart design that requires no permanent modifications to the bike, just clamp around the downtube, and connect the drive hub to some spokes. Clamp the fuel tank under the cross bar... and an accelerator lever to the handlebars... simple!

https://roweryzsilnikami.wordpress.com/1920-je-smith-jes-142cc-auxiliary/

The Cycleaid did a similar easy mounting that was quickly undone when upgrading bikes:

https://roweryzsilnikami.wordpress.com/1951-british-salmson-cyclaid-restored/