the software is so bad it's literally a national security risk.

While I may agree on Sharepoint, not everything from Microsoft is bad. Often the alternatives are even worse.

Really?

Libreoffice Calc and Excel are probably your strongest argument, Excel runs the world after all.

But, if it wasn’t for incompatibility and fear of incompatibility- I have a hard time thinking Calc is materially worse; I doubt theres a single workflow not possible in Calc- and if O365 utils get worse looking then Calc will win there too soon enough.

For everything else in the microsoft stack, either its “this thing does many things thus is incomparable to any one thing!” or its simply worse.

Even the best tools that I would actively defend (MSSQL) are only equivalent to other solutions (PGSQL) and almost never better than everything offered elsewhere.

ok, excluding things they have bought and not yet destroyed. what's good? (we'll accept that xbox is good, distinct and unrelated to the rest of their offerings)

Is there a one stop solution for email, calendars, bookings etc that could run on premise?

Zimbra, Nextcloud Hub, MDaemon (Mail/Cal/Contacts), Group Office and Kopano come immediately to mind.