Check out CoCalc[1], formerly Sagemath Cloud. It is a project with a lot of history (think of SageMath as python-based open-source Mathematica alternative). It supports Jupyter and Sage notebooks.
CoCalc also supports Julia, LaTeX, R.
I'm using Google Colab[2]. It's the direct equivalent, hosted by Google. Not quite open source, but it's free (and does it matter if a cloud service is open source? If you want control that open source gives you, you run things locally anyway). Disclaimer: I work there, and use it at work daily.
For a Colab vs CoCalc comparison, see[3]. In my brief experience, CoCalc UI is currently snappier than Colab; but I haven't written any large notebooks in it yet.
There are other Python cloud services[4] which I don't have any experience with.
[2]https://colab.research.google.com/
[3]https://www.forbes.com/sites/gregoryferenstein/2019/08/18/a-...
[4]https://www.dataschool.io/cloud-services-for-jupyter-noteboo...