Originally a Flobert fired a rimfire cartridge, round ball, no powder- and was one of the very first cartridge firearms. Pretty well limited to pellet gun pressures, and good for target shooting in your living room. There was NO locking mechanism, and the gun relied on the hammer spring to hold the hammer down, holding a LOW pressure case in place when it fired.
Julien WARNANT of Cheratte invented and patented (March 23 1885) a slightly different system with a flip over breechblock. This was just a bit stronger. Larger rounds were made in 7mm and 9mm, using primer only, or 1-2 grains of black powder. These should NOT be fired with any ammo more powerful than that. The 9mm rimfire shotgun shells are for a VERY different gun.
They were made from 1885 up to ABOUT 1920. There are some very pretty, very ornate guns- engraved, carved stocks, etc- and some pretty plain guns as well. Prices have not been real high on these. Many were made in France, more in Belgium. If you remove barrel from stock you may find proof marks- likely ELG in an oval for Liege Belgium, or marks for St Etienne (France)