The stinger pen gun came in .22LR, .22Mag, or .17 RF
I also hear they made a .25 ACP and .a 380 version too.
They fold in half and a trigger drops down. Becuase they fold, the ATF considers(ed?) them a standard handgun.
The Brady wackos and the retards at the VPC had a hissy fit when they found out this thing existed...and pressured the ATF to reclassify it. I was wondering if it ever happened...