What are best examples of well-structured open source products to learn from?

I am working on a product and I would like to get a glimpse on how do teams structure their code, and how do they organize their thoughts with respect to code/stack/production pipeline (e.g. [RASA](https://github.com/RasaHQ/rasa)).

Sinece we are two engineers developing a product, with humbled experience, we would love to see more eye-opening examples that help acquire best practices. Examples can be e-commerce application, preferably a running pipeline in production.

Elasticsearch - https://github.com/elastic/elasticsearch

Google's Guava - https://github.com/google/guava

Sourcegraph - https://github.com/sourcegraph/sourcegraph

Spectrum - https://github.com/withspectrum/spectrum

Django - https://github.com/django/django