RapidMiner is very fine open source software for data mining. Its previous name was YALE.
A couple of years ago, the product was renamed "RapidMiner" with a corresponding holding company name of "Rapid-I". The open source software is still available but there is also a commercial version with support, training and consultancy available. Go here to see it all.
RapidMiner is an "academic grade" meta-product, this is both good and bad. It's good for flexible leading edge experimentation but for mere mortals it is fantastically hard to learn and fantastically hard to use.
For better or worse, I am learning RapidMiner and it helps me to learn if I write things down and try things out. Using a blog forces me to structure properly since I have to pretend I am addressing the content to someone else.