Interestingly, Giles Thomas (the guy behind Python Anywhere) originally developed a Pythonic Spreadsheet application, called Resolver One, and then iterated to a a web-based version, called Project Dirigible.
Python Anywhere eventually span out from Project Dirigible when they realised that it was mostly being used for "generic" Python development rather than being used as a spreadsheet. There's an interesting write-up on this evolution here: https://blog.pythonanywhere.com/197/, and a demo of Dirigible here: https://www.youtube.com/watch?v=2ZoIp-5NaiQ.