The statistical program R has a number of packages that offer another avenue for open source GIS work. I am currently learning the capabilities using the text An Introduction to R for Spatial Analysis & Mapping, by Chris Brunsdon and Lex Comber.
Eric Anderson produced instructions on how to create thematic maps of US counties for his course on Reproducible Research, which can be found here. Also, it is possible to process some R commands through the web browser tool Snippets on rdrr.io. An example of creating maps of the US and New York counties is shown below, using the code from Eric Anderson’s course.