Pi-hole

Pi-hole sits between your devices and the internet as a DNS sinkhole: ads and trackers are blocked for every device on the network — smart TVs and phone apps included — with nothing to install on the clients.

It runs on almost anything, famously including the Raspberry Pi it is named after. Honest expectations help:

• DNS blocking cannot remove YouTube ads or anything served from the content's own domain.
• Some sites and apps break and need whitelisting; the household will let you know.
• The admin dashboard makes query analysis genuinely interesting.

One of the classic first self-hosting projects, and still one of the highest-impact ones.