[williamstein]

SageMathCloud (https://cloud.sagemath.com) using a Jupyter notebook with the R kernel, or a Sage worksheet in R mode. (Disclaimer: I work on this.)

SageMathCloud is somewhat similar in functionality to DataJoy + ShareLaTeX, ShareLaTeX is by the same people as DataJoy, and I think ShareLaTeX is not shutting down anytime soon. I had always wondered why they built DataJoy as a separate product, rather than just expanding the functionality of ShareLaTeX. In the case of SageMathCloud, I built something more like DataJoy first, then expanded the functionality to cover LaTeX typesetting, rather than making a separate product. Also, SageMathCloud is 100% open source.

I recently posted https://news.ycombinator.com/item?id=12169979 here which was really about having several separate products using similar technology but different names, versus having one big product.

[williamstein]

DataJoy is also similar to http://sagecell.sagemath.org/, which requires no sign in and lets you run Python (and much more) directly from a website, is pretty battle tested at this point, and is entirely free to use and open source. Disclaimer: I pay for some hosting of SageCell.