I disagree. My research suggested that Amazon's policies about open source and game development were stricter. (For example, I must be willing to disclose any sales data to Amazon. I must use Amazon products when possible. I must make my project available on the Amazon store if possible.) Most companies also have a process to keep copyright if you need/want to.

Yes, most companies have approval processes. They might even be onerous approvals processes. Amazon expressly forbid me from participating in game jams with people who were not in my org.

>I disagree. My research suggested that Amazon's policies about open source and game development were stricter.

Worked at microsoft for 2 years, there are the same policies. It was not contractual though. It's just that there were notes broadcasted saying that whenever you discussed with third parties, you should use microsoft tools if possible. Want to meet someone? Send a Bing Maps link, not Google Maps. Want to share a research? Send a Bing Link, not a Google search. etc.

As for the confidentiality clauses, I work in finance, and the rules on IP and personal projects are the same as what you describe.

Today I learnt that there is a Bing Maps

Microsoft have been very helpful to OpenStreetMap. Since 2010 they allow the OSM community to trace from the Bing aerial imagery to add things to OSM. Roads, buildings, everything you can see with the aerial imagery. It's fantastically useful. OpenStreetMap database would be a fraction of the size if it wasn't for Microsoft granting us this. As of July 2018, they allow us to use Streetside imagery too. (Alas you can't use the actual maps, just the aerial/satelite imagery)

Yahoo allowed tracing from 2007 till 2011.

Microsoft is big and the contacts I have there tell me that the open source policies vary by department.

Microsoft has also undergone a massive transformation over the last few years with respect to OSS.

Most companies being who exactly? All the people disagreeing with me clearly have not read their terms of employment.

Maybe qualify “most companies” to “most large Silicon Valley tech companies”? I’ve never worked anywhere with any non-compete clause at all.

The last 4 places I've been, three encouraged us to participate in FOSS. Only one was neutral, but disallowed paid side gigs (open source was ok). It's anecdata, but totally opposite of your experience.

Nope, first time ever I hear about something such restrictive. That by itself would be a reason for me to not sign an employment contract with Amazon.

Yeah. Amazon loses a small but significant number of potential hires when they learn about the open source clause - often very good people, too. When I left they were actively working on trying to find a solution, as it had been a thorn in the side for years.