let me say: tempus fugit.
mongox - DEPRECATED
mongo - 0.5.4 December 1, 2015 (docs)
mongodb_erlang - seems not to support op_msg (since 3.6)
Unfortunately, the libraries are not up-to-date regarding the MongoDB server. Since I use the latest version of my projects and therefore want to use the features of the server, I was looking for a suitable driver. Unfortunately I did not find one, so I searched for the best starting point and developed my own driver.
