This week version 2.0 of the mongolite package has been released to CRAN. Major new features in this release include support for MongoDB 4.0, GridFS, running database commands, and connection pooling.
Mongolite is primarily an easy-to-use client to get data in and out of MongoDB. However it supports increasingly many advanced features like aggregation, indexing, map-reduce, streaming, encryption, and enterprise authentication. The mongolite user manual provides a great introduction with details and worked examples.