Pharo[1]. It's an actively developed Smalltalk dialect. There's a MOOC[2] on it, a superb data visualisation engine with Roassal[3] and a free book dealing with mathemathical algorithms[4] implemented in Polymath. The environment is a great experience to code in, for example, you can actually search a method just by giving a example of what you want to do.
[1].
https://en.wikipedia.org/wiki/Pharo [2].
https://mooc.pharo.org/ [3].
http://agilevisualization.com/ [4].
https://books.pharo.org/numerical-methods/