Nanopb is a plain-C implementation of Google's Protocol Buffers data format. It is targeted at 32 bit microcontrollers, but is also fit for other embedded systems with tight (2-10 kB ROM, <1 kB RAM) memory constraints.
Latest stable releases
The development happens in GitHub repository (browse repository):
git clone https://github.com/nanopb/nanopb.git
Bugs can be reported on the GitHub issue tracker.
There is a discussion forum on Google Groups. Please ask any questions there.
The zlib license:
Copyright (c) 2011 Petteri Aimonen <jpa at nanopb.mail.kapsi.fi>
This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.
Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
As of 2015, protobuf-c is the most viable alternative, should you require something more than what nanopb can provide. It has more complete support of Protocol Buffers features (such as easy to use unbounded recursive messages), but relies on dynamic memory allocation and the code size is quite large (more than 20kB binary).
There are also several other projects that aim to create a Protocol Buffers implementation suitable for embedded use. As of 2015, they all seem to be unmaintained: lwpb Protobuf-Embedded-C empb.