seasonal is an easy-to-use R-interface to
X-13ARIMA-SEATS, a seasonal adjustment software developed
by the United States Census Bureau. X-13ARIMA-SEATS
combines and extends the capabilities of the older
X-12ARIMA (developed by the Census Bureau) and the
TRAMO-SEATS (developed by the Bank of Spain) software
packages. The best way to start is to have a look at the vignette:
vignette("seas")