The Community Supported drivers page (http://docs.mongodb.org/ecosystem/drivers/community-supported-drivers/) for the 'R' drivers needs some work:

Incorrect link for 'rmongodb' driver
The page points to https://github.com/gerald-lindsly/rmongodb
This URL no longer exists. It would appear the project has a new maintainer and now lives here: https://github.com/mongosoup/rmongodb

Description for 'rmongodb' driver
The associated description states "Full featured R interface to MongoDB built on top of the mongodb.org supported C driver" but this driver uses version 0.7.1 of the legacy C driver and hasn't received any updates in 10 months, so may not be as fully featured as described.

Name of 'RMongo for R client' driver
The second driver listed is called 'RMongo for R client' but the CRAN page calls it "RMongo: MongoDB Client for R" which seems like a better name.