Depends.
If usable, clean install of a new OS, and donate to someone who would otherwise not have a system.
or
A media center for your house.
or
A whole house firewall box.
or
a disposable testbox, that you can wipe as needed. I have a now 10 year old low end Toshiba, that I used for initial Win 10 testing when it was first released.
However, I also have a kneehigh+ stack of laptops in the garage, that are absolutely no longer usable. Various levels of broken, or simply too old.