Ask HN: What are some open source APM tools?

I was looking for some APM tools to integrate with my nodeJS SaaS app (NodeJS backend, React Frontend) and I was unable to find any that were open source.

The closest I found was Sentry which is not really an APM tool as much as an exception logging tool. The only other tools that I've found are Raygun and Opbeat - both of which are really nice to use, but I would definitely prefer to support opensource and also host it myself.

What are some open source APM tools that you use?