Terminal command ncdu
No, ncdu is not natively available in OSX. But, if you want it, you can install it via homebrew. You just need to type the following to install it:

brew install ncdu


This is the version available:

$ brew info ncdu
ncdu: stable 1.10, HEAD
http://dev.yorhel.nl/ncdu
Not installed
From: https://github.com/Homebrew/homebrew/blob/master/Library/Formula/ncdu.rb