ProbLog is a simple language for probabilistic reasoning. It allows you to write logic programs that account for uncertainty among the facts and propositions, and it can calculate the probabilities of hypothesis or events based on your model. An online tutorial with a web-based calculator is available here.
Of all the intellectual techniques available for those who pursue a rational worldview, I believe none are more important that Bayesian inference. By saying this is “most important,” I don’t mean to disregard the fundamentals of logic, mathematics, probability, statistics, etc — those are all prerequisites to understanding Bayesian techniques. There’s been a lot of talk about Bayesianism recently in skeptical circles, with Richard Carrier drawing a lot of attention for his advocacy of Bayesian methods in history. I appreciate that there are a lot of philosophical arguments surrounding Carrier and others’ use and application of Bayes’ theorem. As with all reasoning techniques, Bayesian reasoning can be used well or it can be used poorly.