Weka

Weka is a classic, open-source machine learning software written in Java. It contains a collection of visualization tools and algorithms for data analysis and predictive modeling. While it is older than many modern tools, it remains a staple in academic research and is highly effective for teaching machine learning concepts. It provides a comprehensive suite of tools for data pre-processing, classification, regression, clustering, and association rules.

It is a reliable, free tool for those who need a stable environment for traditional machine learning tasks.