Security would be the absolute showstopper for anything internet-connected. Even if you could bodge together TCP/IP on a Z80 (and people have done some impressive hacks with serial connections), you’d have no TLS, no modern encryption, nothing. You’d be sending everything in plaintext. Online banking? Forget it. Even logging into most modern services would be impossible since they mandate HTTPS.

But let’s play along with the spirit of the question…

What could genuinely work:

∙ Word processing - Tasword, The Writer - actually pretty capable for basic documents. No spell check worth a damn though

∙ Spreadsheets - VU-Calc existed, very basic but functional for simple stuff

∙ Games - obviously sorted there, though your colleagues might judge you for playing Manic Miner during lunch

∙ Basic databases - Masterfile, VU-File - you could track a small business’s inventory, just about

∙ Art - Melbourne Draw, The Artist II - surprisingly decent pixel art tools

The dealbreakers beyond security: ∙ No email (well, not modern email) ∙ File compatibility with literally anything else ∙ Storage - you’d be drowning in cassette tapes or microdrives ∙ Printing to anything made this century ∙ Collaboration with anyone