Yes, in short. The core Android operating system itself is Open Source, technically anyone can fork it into their projects. But there are certain limitations. The Android Open Source Project (AOSP) provides common, device-level functionalities. Google Mobile Services (GMS) is a collection of Google applications and APIs which is not included in the Android Open Source Project (AOSP).
However, in real life, you will always need a mobile device management solution for the deployment of Android Open Source Project (AOSP) in quality devices. Otherwise, the product OS will not get any updates and bug fixes.
There are forks from the Android Open Source Project (AOSP), usually by the mobile device management solution providers, such as emteria.OS. These operating systems are ready to be used for commercial products with additional applications and services.
Manufacturers need a license to ship with Gmail, Google Maps and the Google Play store pre-installed. They are called Google Mobile Services (GMS). Although Google does not charge for GMS, you will need a certificate from an authorized testing facility. Companies such as Samsung, Sony etc pay these costs to pre-install Gmail, Google Play and other parts of Google’s mobile services. The cost can be $40,000 for 30,000 devices.
Can I use Android Open Source Project Without Google’s Mobile Services For Free?
Shipping with Google Play pre-installed is illegal without the license. That severely restricts the “Android feel”.
Most of the terms are described here:
Probably Google wants to say to use its UI for commercial products, not blindly copy them:
Android is based on the Linux kernel. That is the big reason why the Android Open Source Project (AOSP). But the UI we see on the devices of Samsung, Sony, Xiaomi, Oppo, and many other manufacturers are practically created from scratch.
Android is like a closed-source platform where the application repository requires a license. Like Debian and Ubuntu are two different distributions, Samsung’s Android and Vivo’s Android are two different distributions. Samsung’s main interest probably is around Tizen. On Sony’s devices, you’ll see the stock Android. That is not like Samsung’s Android with One UI .
If you are developing a device and OS fork and related software for commercial intention, you should get a clear opinion from an attorney for protection. Probably you have to add a EULA. There are many alternatives which are forks such as LineageOS, Sailfish OS, and Ubuntu Touch. Similarly, Tizen is open-source software, but there are proprietary components owned by Samsung and probably it is a difficult platform to develop things.