Many tech workers have old monitors or tablet screens sitting unused on their desks.
Create a customizable dashboard system that gives these displays purpose - showing system stats, calendars, or feeds in retro computer aesthetics (like old Mac OS).
Sell premium themes and advanced data source integrations. Offer a free basic version.
Start with macOS support (shown in example), then expand to Windows/Raspberry Pi.
Risk: Very niche audience with limited willingness to pay for something that's mostly cosmetic.