Licensing and Openness

How open or proprietary each operating system's source and development model is.

Linux

Free and open source under the GPL, developed transparently by a global community and companies collaborating in the open; anyone can read, modify, and redistribute the kernel and most of the surrounding userland.

Windows

Proprietary and closed-source; Microsoft controls development entirely, and while some components (like parts of .NET or the Windows Subsystem for Linux) are open source, the core OS itself is not.

macOS

Proprietary, though built on top of the open-source Darwin core, which Apple publishes separately; the user-facing OS, frameworks, and apps on top of Darwin remain closed and controlled entirely by Apple.

iOS

Proprietary and the most tightly controlled of the group; Apple governs the OS, the App Store, and the review process with no meaningful open-source component exposed to end users.

Android

Its core (AOSP) is open source under the Apache License, but most real-world devices ship with proprietary additions on top — Google Mobile Services, the Play Store, and manufacturer customizations that aren’t part of the open project.

ChromeOS

The underlying Chromium OS project is open source, but commercial ChromeOS devices bundle proprietary additions (Google sync, Play Store, licensed codecs) on top, similar to the relationship between Chromium and Chrome.