Ask HN: What's something I can do with a spare, modern laptop?

Install Linux and attempt to do advanced stuff that just work in Windows and Mac but requires tweaking Linux. Spend hours looking for solutions on the Internet. Then brag about your achievements online.

Donate it to a deserving non-profit in your area.

Virtual fish tank: go to youtube, load a video of a real fish tank and watch it.

For personal use: Mine bitcoins. Run as VPS. Host websites for local businesses. Charge for usage. If you have GPU, then sell usage by hour for Deep learning students.

For social good: Donate to old age home.. arrange a sharing schedule between a group of students who can't afford.. mine bitcoins and donate what you earn.. work with a local shop to arrange internet access and support unprivileged people to find jobs online .. donate to a prison .. lotsa options though I am not sure if you meant give away ..

Install an OS you haven't used before and learn more stuff?

Energy efficient home server with built-in battery backup.

Maybe donate it? A school, library or student may need one.

HTPC

Home firewall

learn to BSD