Here is a set of derailleurs arranged approximately with age.
To the right are Cyclo Benelux coil-spring type derailleurs. They went through several design changes from the 50's - 60's and were based on earlier French efforts. In the middle is the nicely-named Resilion Crimson Star which was both inexpensive and worked quite well, next to which is a Cyclo rod-type front derailleur. To the left is a mid-1950's Campagnolo Gran Sport, an early 1970's Nuovo Record (soon to be on a bike) and a second-generation Campagnolo Rally. At the extreme left is a second generation C-record and a 1980's Chorus.