Internet Archive - Very useful for general usage internet but not for specific needs (check fmhy).

Have I Been Pwned? - Periodically use this to check whether your email/online presence is compromised or not.

Bitwarden (or if you want to self-host it use Vaultwarden) - Personally I used this password management so I can keep my pass and you can auto generate passwords with custom parameters if needed.

Curated OSINT resources - You want to ID someone online? this resources can help you to do so, though you also need to understand the basics. It may not work if person you’re looking for does not have a much online presence.