what is this?

massgrave.dev

... and what is this?

From massgrave.dev, just below the big heading:

Open-source Windows and Office activator featuring HWID, Ohook, TSforge, and Online KMS activation methods, along with advanced troubleshooting.

it is in the name get.activated.win(dows)

Microsoft doesn't care if a home or hobbyist user uses this, because enforcing the license against such a user is not worth it as the payout wouldn't even cover their own effort/lawyers.

Microsoft may absolutely care if you use this at work (even by accident, by bringing your personal machine to the office) since that's where they can collect a decent amount of money for a license breach.

speaking from office / work perspective microsoft is actually not the company that cares either, you receive a bounty/payout for reporting license violations within your company.

IANA (iamnotamerican) so cannot really confirm except for 2nd hand knowledge, but in my european country every company I've been around in just uses pirated everything.

Also this is a tool that breaches several agreements and laws, including the particulary nasty one of DMCA (breaking digital locks) if anything this is the one thing microsoft should care about rather than individual users breaking said license.