I used to fit several different makes of towbars and I can't think of one that you could detach. However, you can remove the actual towbar hook-up by removing the two bolts holding it in place. Do you mean this?
Volvo and Peugeot are just two manufacturers that fit their cars with detatchable tow-bar hook-up ball type things. I'm sure many other manufacturers have been offering this as an option when new for some time. This means that there are many second hand cars with them fitted.
Volvo towball and lighting assemblies are detached with two clevis pins and have a nice body-coloured moulding to fit over the exposed towbar mountings when you are not using the car for towing.