"GNU PSPP is a program for statistical analysis of sampled data. It is a free as in freedom replacement for the proprietary program SPSS, and appears very similar to it with a few exceptions."
R based GUI. Very powerful and flexible. You need to open from R or RStudio. "Rcommander Rcmdr a simple GUI interface for R"
Easy to use (easiest, perhaps) R based GUI. Completely self-contained and open. Wonderful tool to use. "jamovi is a new "3rd generation" statistical spreadsheet. designed from the ground up to be easy to use, jamovi is a compelling alternative to costly statistical products such as SPSS and SAS."