sprex is a package for calculating species richness for rarefaction and extrapolation.
To install the stable version from CRAN:
install.packages('sprex')
To install the latest version from GitHub:
# make sure you have Rtools installed
if (!require('devtools')) install.packages('devtools')
# install from GitHub
::install_github('ericarcher/sprex') devtools
You can see the most recent changes to the package in the NEWS.md file: https://github.com/EricArcher/sprex/blob/master/sprex/NEWS.md