My favorite Opensource data mining software, Rapidminer, rose from third place to first place in 2013 KDnuggets’ preferred software poll.
If you want to see the power of Rapidmine there is a great tutorial, below, on decision trees. A decision tree takes a data set and creates a visual representation of decisions and their probable outcomes. You can see from this tutorial how easy Rapidminer is to operate. Decision trees good for guessing the outcome of a decision and is probable result. The tutorial takes a dataset of marketing mailers and determines the best way to get the desired results, based upon a sample dataset.
Data Python packages (my second favorite) slipped in the poll, but like any software math nerd, I take this as a badge of honor. Since it is non-visual and a scripting language, it is more for the programming nerd. This does show how the data-mining industry is changing. More gui based programs are becoming more popular bringing data-mining to the average person. Excel has an extremely easy to use datapack, which is on the kdnuggets list. The average person can take an Excel table and in minutes run a regression test on it, leap years from when I learned statistics.