It looks alike the frame of a 63 or 64 (made only 2 years) Schwinn "Bicycle built for Two" with different forks and everything else. Look for a serial number on the left dropout. After they made these, both front and rear rider were step through and they called them Schwinn Twinns. The part where the chain idler bolts on is missing, if that's one of those frames. Here's one I had some years ago.