I saw this post on Reddit this morning and I've been doing some thinking:
It is a series of locks such that if any one is removed then the gate can be opened. Possible uses for this are when multiple companies need access to the same road. One advantage that this has over using just a combination lock is that if one company needs to change its lock (maybe to protect itself from an ex employee) then they can just change their lock without having to interact with the other companies.
In a sense this is the lock equivalent an OR gate. It opens if any of the inputs (in this case keys) are provided. Looking around the internet here are some other examples:
To understand this one you have to understand that the leftmost chain is welded to the bolt, while all the other links are only connected to each other through padlocks. Here's a GIF showing an example:
This example is much easier to see how to extend. If we wanted to recreate an AND gate component then we could have more than one bolt each built in a similar style. This means that you could build any level of complication, such as a system where you need any 2 out of 3 keys.
Here's another OR gate stripped to its bare bones:
Each padlock acts as a link in the chain.
Finally let's look at a pure AND gate in lock form:
These are frequently used for dangerous electrical equipment that is required by law to have certain engineers present for their operation. However if you want to put a piece of treasure in a tontine (which are illegal, but so interesting) then this is the sort of lock that you want.