Shameless but relevant plug: I built CodeApprove (https://codeapprove.com) to bring the best parts of the Critique workflow to GitHub PRs. Obviously there are many things that don't translate (Google doesn't use git, and it has insane CI/CD integration) but CodeApprove gives you the same workflow. You always know which conversations are resolved, which PRs need your attention, etc.
Feel free to reach out via email if you're curious.
I'm a former Google developer and current CodeApprove customer, and I just want to endorse CodeApprove. They're the closest thing I've found to Critique outside of Google.
The UI is really straightforward, and Sam (the founder) has been responsive to feedback.[0]
I have no relationship with the company except just being a satisfied customer.
Feel free to reach out via email if you're curious.