https://gitmate.io - Gitmate is made by a friend of mine and it's pretty good. It uses coala [1] underneath (coala is a unified static code analysis tool that supports 100+ languages; I'm a maintainer, so shoot me any questions you might have about coala).
Gitmate is much more than just static code analysis and review suggestions. It supports automatic issue triaging, rebases, labeling, identifying human reviewers, and so on.
Here's an example code review: https://i.imgur.com/JO0nXL7.png
(Here's an example if there are 10+ reviews: https://i.imgur.com/VlQA9iS.png)