Notch on seat stay
 

On my old steel frame there is a little notch on the right seat stay about 100mm from the drop out. I couldn't figure out what this little notch is for until I took the wheel off for service, alas there is something to hand the chain nicely. Can't find this on new frames.

Yeah. I had an old steel MTB frame with a chain hanger too. Much like how most bikes these days no longer come with fender mounts, rack eyelets and pump pegs, these little things seem to have been judged as unnecessary by bike manufacturers. Some old school frame makers still include them however. Rodriguez Cycles even includes a bottle-opener on their seat stays. ;)