Sometimes it’s annoying if you have a large number of keys to carry around (a certain German research student I used to know claimed that having lots of keys was a sign of personal liberty, but I resist any such suggestion (cf having a lot of guns)).
Today’s invention is to form a sprung key ring into the head of each key. This saves weight and allows keys to be arranged in a chain, or even a web, rather than acting as ‘petals’ on a central ring (which can make finding the right key, let alone turning it, rather difficult).
Another example of someone reinventing an IOTD:
http://www.core77.com/blog/object_culture/keyring_in_the_shape_of_a_key_duh_13990.asp
These people seem to have come up with this in July 09, so I still claim inventorship. http://www.keybrid.com/