There is one MongoDB client for Clojure that has been around since 2009. So, why create another one? Monger authors
wanted a client that will
* Support most of MongoDB 2.0+ features but only those that really matter. Grouping the way it is done today, for example, does not (it is easier to just use Map/Reduce directly).
* Be well documented.
* Be well tested.
* Be maintained, not carry technical debt from 2009 on and on.
* Will integrate usage of JavaScript files and ClojureScript (as soon as the compiler gets artifact it is possible to depend on for easy embedding).
* Will learn from other clients like the Java and Ruby ones.
* Will target Clojure 1.3.0 and later from the ground up.