I used https://cloud.sagemath.com/ https://cloud.sagemath.com/ entirely to implement https://cloud.sagemath.com/ https://cloud.sagemath.com/ itself (along with

I used https://cloud.sagemath.com/ https://cloud.sagemath.com/ entirely to implement https://cloud.sagemath.com/ https://cloud.sagemath.com/ itself (along with a dozen other collaborators, of course). I've probably spent thousands of hours coding via cloud.sagemath.com at this point. Probably my favorite feature of cloud.sagemath.com is TimeTravel, which Jonathan Lee first implemented as a Google Summer of Code project, which lets you browse (at very high resolution) all past versions of your document, and see diffs between two points in time. I also like having a separate chat associated to every document, and realtime collaboration (with multiple cursors). A lot of our users do education, research, and data science, so we support course management, latex, and Jupyter notebooks. But SageMathCloud is also useful for software development.