Is open-source software? Can we self-host?

Hi there.

I’ve got to know due to introduced on a tech blog written in Japanese language. It post said “ is open-source software”.
Another post on Github “Awesome open-source alternatives to SaaS”, is listed as open-source software.

Although, I have been looking for install local or self-hosting docs for, but I could not find out. Strangely, if is open-source, there should be the docs for Docker, system requirements, use runtimes for example Node.js, Ruby, PHP etc…

So, “ is OpenSourceSoftware” is incorrect? Is the correct fact “ is proprietly SaaS software, core source code is closed. And SDKs and some stuffs are open-source.”?

This forum topic related self hosting, but it seems to be an answerer replied misguided. We know that our app can be self-hosted by us, it is so naturally. I want to find out that can we self-host it self.