The source code for Android is open-source:
it is developed in private by Google, with the source code released
publicly when a new version of Android is released. Google publishes
most of the code (including network and telephony stacks) under the non-copyleft Apache License version 2.0. which allows modification and redistribution.[185][186]
The license does not grant rights to the "Android" trademark, so device
manufacturers and wireless carriers have to license it from Google
under individual contracts. Associated Linux kernel changes are released
under the copyleft GNU General Public License version 2, developed by the Open Handset Alliance,
with the source code publicly available at all times. Typically, Google
collaborates with a hardware manufacturer to produce a flagship device
(part of the Nexus series) featuring the new version of Android, then
makes the source code available after that device has been released.[187] The only Android release which was not immediately made available as source code was the tablet-only 3.0 Honeycomb release. The reason, according to Andy Rubin in an official Android blog post, was because Honeycomb was rushed for production of the Motorola Xoom,[188]
and they did not want third parties creating a "really bad user
experience" by attempting to put onto smartphones a version of Android
intended for tablets.[189]
Only the base Android operating system (including some applications)
is open-source software, whereas most Android devices ship with a
substantial amount of proprietary software, such as Google Mobile Services, which includes applications such as Google Play Store, Google Search, and Google Play Services – a software layer that provides APIs
for the integration with Google-provided services, among others. These
applications must be licensed from Google by device makers, and can only
be shipped on devices which meet its compatibility guidelines and other
requirements.[65][108] Custom, certified distributions of Android produced by manufacturers (such as TouchWiz and HTC Sense)
may also replace certain stock Android apps with their own proprietary
variants and add additional software not included in the stock Android
operating system.[3] There may also be "binary blob" drivers required for certain hardware components in the device.[3][99]
Some stock applications in AOSP code that were formerly used by
earlier versions of Android, such as Search, Music and Calendar, have
been abandoned by Google in favor of non-free
replacements distributed through Play Store (Google Search, Google Play
Music, and Google Calendar) that are no longer open-source. Moreover,
open-source variants of some applications also exclude functions that
are present in their non-free versions, such as Photosphere panoramas in
Camera, and a Google Now
page on the default home screen (exclusive to the proprietary version
"Google Now Launcher", whose code is embedded within that of the main
Google application).[3][190][191][192]
Richard Stallman and the Free Software Foundation have been critical of Android and have recommended the usage of alternatives such as Replicant,
because drivers and firmware vital for the proper functioning of
Android devices are usually proprietary, and because the Google Play
Store application can forcibly install or deinstall applications and, as
a result, invite non-free software.[193][194]
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