Weird egg - anyone else had one like this?

No, they do lay wierd eggs sometimes. It won't be the last I don't suppose. It's called a "lash" I think

Birds eggs are little biological miracles ! I am suprised that we do not get more with defects.

Where would you start to design a machine to make one !

It looks like a softie which can be due to a scare during the egg production, even windy weather can cause the hen to pass the egg too quickly for the shell to form properly.  Other reasons could be lack of calcium intake due to molting.  Hopefully it will be a one off but it is always best to keep an eye on these things.