It's a Maillard Helicomatic Diabolo rear hub for an MTB or touring bike. It's age you can guess from the fact it has only 5 gears and MTB's were expected to have bolted rear hubs, not Q/R! The Helicomatic system, for thos too young to remember was a valient attempt to solve the problem of freewheels winding tight onto the hub thread and not only needing special removers but often a BIG spanner to shift them. This freewheel span onto the helix on the hub and was held on by a lock rick which on most versions only required a small ring spanner tool to remove. Also the hub bearing was in a better position, outboard near the dropout, preventing axle breakages that happened sometimes with freewheel hubs. The Diabolo was a version that did away with the special tool by using the finger friendly <sic> lockring seen in the pictures.
This was all of course to allow you to change broken spokes easily on the freewheel side of the hub - which happened a LOT more in those bad old days. Surprisingly the idea worked really well except that it cost a lot more than normal setups and was hard to find spares for in the UK.
Also, being French, Maillard made all the parts (spline size/spline diameter/sprockets etc) on the MTB/Touring Diabolo hub incompatible with the road version of the hub...
So, it didn't catch on... especially as freehubs came along and solved some of the problems with freewheel hubs. This is the only Diabolo I've seen, which I obtained from a touring friend back in the 90's although the road version had many adherents in Europe back in the 80's/90's.Whatever, this one is probably going to be kept as a curiosity but I'm building a pile of stuff I'm going to have to sell somewhere at some point.
For those wanting more info try:
https://borgercompagnie.com/helicomatic/specs.html
Richard