[Kokouane]

It's high overhead, but having a VM just for Excel isn't that insane. Performance differences these days are negligible, and if you are just using Excel I doubt it's that much of a problem. There is also Google Sheets.

For planning, Jira is king and available as a web app.

[tourmalinetaco]

Why do you need specifically Excel? Why not literally any native sheet application, most of which can save to .xlsx?

[yttribium]

Large chunks of the world economy run on specifically Excel.