This is the Syncthing project which pursues the following goals:
Define a protocol for synchronization of a folder between a number of collaborating devices. This protocol should be well defined, unambiguous, easily understood, free to use, efficient, secure and language neutral. This is called the Block Exchange Protocol.
Provide the reference implementation to demonstrate the usability of said protocol. This is the
syncthingutility. We hope that alternative, compatible implementations of the protocol will arise.
The two are evolving together; the protocol is not to be considered stable until Syncthing 1.0 is released, at which point it is locked down for incompatible changes.
Take a look at the getting started guide.
Getting in Touch
The first and best point of contact is the Forum. There is also an IRC
#syncthing on freenode (with a web client), for talking
directly to developers and users. If you've found something that is clearly a
bug, feel free to report it in the GitHub issue tracker.
Building Syncthing from source is easy, and there's a guide that describes it for both Unix and Windows systems.
As of v0.10.15 and onwards release binaries are GPG signed with the key D26E6ED000654A3E, available from https://syncthing.net/security.html and most key servers.
There is also a built in automatic upgrade mechanism (disabled in some distribution channels) which uses a compiled in ECDSA signature. Mac OS X binaries are also properly code signed.
Please see the Syncthing documentation site.
All code is licensed under the MPLv2 License.