This is exactly what we built Mira for. It's self-hosted, bring-your-own-model/BYOK, and most importantly, open source.
You point it at your own API keys (e.g. OpenRouter or a local model) so nothing leaves your infra, and it runs as a code reviewer on PRs.
It's also ridiculously quick at reviewing (benchmarks at ~77s) because your PRs aren't sitting in a queue on a cloud somewhere (alternatives are > 5 minutes)
We're working really closely with our users to build the best possible code reviewer. Feedback and contributions are highly encouraged.
What I use for: I use for identifying duplicated code. It is deterministic, doesn't use AI, offline, runs from CLI and is super fast (and free).
What I dislike: I won't say it I dislike, but it is not a tool that does all the jobs of a code review. For instance, it doesn't flag security issues. It is superfocused on code duplication (it performs better than Sonar for this use case) and is specifically useful for large codebases. Disclaimer: I am one of the collaborators, so take it with a grain of salt https://github.com/Rafaelpta/dupehound
As my daily driver at home, I use Pi though because it doesn't get in your way and forces you to understand how the sauce is made.
Codex on top of that with specific rules and syntax requirements.