Install through Home Brew

brew update && brew install mongodb

Create a data folder

mkdir -p /usr/local/Cellar/mongodb/YOUR_VERIONS/bin/mongod/db 

Setup an alias for starting up our MongoDB

alias mongoup='/usr/local/Cellar/mongodb/2.6.6/bin/mongod --dbpath db'

Using it

$ mongo
>show dbs

Shell-centric cross-platform MongoDB management tool: http://robomongo.org/