Squiggle is a special-purpose coding language for generating probability distributions, estimates of variables over time, and similar tasks. It was developed by the Quantified Uncertainty Research Institute.
The official basics guide is a good written guide if you have experience programming and/or have a specific project in mind already.
Note that squiggle is still in development and has several known bugs.
Squiggle official website.
Squiggle basics guide
Squiggle components: tools to implement squiggle into websites
Squiggle Tweaker: Simple squiggle visualiser
Squiggle to Graph [WIP]: generate visual dependency graph of squiggle code