I like to building things and have this as a fetish (although, I'll admit, only when it's done by a female) and there is an area where both of these overlap.

I have an idea for an adjustable chair with a few straps for limb/abdominal restraints. Initially, the guy (or girl if you wanna take turns) would sit down in the device that looks like a normal chair and their partner would strap them in to restrain the thighs (just above the knee), lower legs, upper arms, forearms, lower abdomen, and torso. After that a crank would be turned that opens the leg rest and pulls the knees apart to a maximum of 50 degrees off center. Another crank would be turned to adjust the lean of the individual in the chair and a third would be turned to adjust height to allow the balls of the occupant to be at the perfect height for the individual to bust them either by kicks or punches without the occupant being able to react to protect them allowing for multiple rapid hits.

I know etsy sells stuff that people make, is there a site similar to that where things can be sold that have an adult flair to them?