I've been at Red Hat so long now (12 years) that it can be easy to take things for granted, but the biggest thing is just how open and transparent a company it is. There's not a lot of silo's or little kingdoms fighting each other, we're all generally working together.
For example, we're a fairly large company (10000+), but we still have an all company mailing list. And it is used by anyone to raise a concern, talk about an opportunity, etc. And that starts a conversation with anyone participating. I am on the Services side, but there is no barrier in place for me to reach out to anyone in the BU, Engineering, Marketing, whatever. I don't think I have ever had to pass a message up the chain of command for it to be passed down somewhere else, I'm just allowed to communicate when and how I need to.
The other way it comes out is that open-source has truly warped our way of thinking about things. For example, there's not a culture of restricting access to our own documents, team drives, etc. One of my peers was working on a new slide deck on a team drive, hadn't really shared it with anyone, then found out that one slide was copied into a presentation done by an EMEA team a day later. That kind of easy access and reuse is just _standard_. It applies to code, but also everything else we do.
I've worked with lots of clients through my job, and it is always eye opening when their employees are worried about "sticking out their neck" or otherwise rocking the boat. Or companies where a developer trying to talk to the business would be an incident with your manager giving you a talk. This is just completely foreign to anyone at Red Hat.