ldapauth is a Node.js script which I have been using for the last 12+ years mostly unchanged.

It started its life in a LXC container, eventually was moved to a Docker container and recently ended up in its own repository on GitHub.

The functionality it provides is not extraordinary, but helped to bridge a gap where no other product was available.
It talks LDAP one one side (although limited to handle user lookup requests) and on the other side connects to a MongoDB database where the information is stored.

It emerged out of the desire to have an easy way to manage individual user accounts for my home WiFi. I already had MongoDB running for some other personal project and simply added the list of users there (including the UI for managing them).
Thus the missing part was to get the WiFi accesspoint to lookup user accounts in MongoDB.

Of course WiFi accesspoints do not directly talk MongoDB, but rather some other protocol like RADIUS.
A freeradius server was quickly setup, but still couldn't talk to MongoDB at the time. Thus comes in ldapauth, which takes LDAP queries from freeradius and turns them into MongoDB lookups so that in the end the WiFi accesspoint receives the user accounts :-)

Not sure if this is particularly useful for anyone else, but at least here it did provide good services (and continues to do so).
Current score is that it has survived three different WiFi accesspoints and has been running on 5 different servers over the time.