[Android Apps and Games] BoneWithABeagle:
Yes, Syncthing can also sync on the local network (local peer discovery) without needing the external announce server. Can't speak for the Android port though.

Since the developer didn't reply....

I/SyncthingNativeCode(21290): [HBRW6] 09:29:25 WARNING: puller: final: chmod /storage/sdcard1/sinting/.syncthing.bash_cheat_sheet.pdf: operation not permitted

Attempting a chmod on a FAT filesystem (the sync folder is on the SD card) is doomed to fail. I think the developer will have to do a lot more than just wrap a native Android UI around the "Linux/ARM" commandline binary to make it properly work on Android.

Apart from that, it seems that a lot of the other problems of the Android version relate to the SD card restrictions of KitKat (locked down SD card access for apps).

I'm syncing a "repo" (to stick to Syncthing's naming covention of "shared folders") with ~9K files between four systems (2 desktop computers, 2 ARM boards, one ODroid-XU and one Jetson TK1, running Linux). No problem there, though the initial indexing may take a while, depending on the speed of your CPU of course, if you have a lot of files in there or if you dump a lot of files into it. I didn't test yet to see if there's a file limit that makes Syncthing bomb out (BTSync will bomb with >100K files in a share), but feel free to try.

And yes, Syncthing also supports a "read only" type of share. You can define a "master repo" that will only sync down to the client peers but not sync any alterations back.

Maybe snoop around on the Syncthing Website, they have a excellent documentation and issue tracker up and running, and the community is outspoken helpful.

Also, Syncthing can replace BTSync. I switched away from BTSync quite some time ago (after I got fed up dealing with the BTSync 1.4 trainwrecks) and didn't regret it; though I have to say I really have no use for syncing with Android, if I need to transfer something over to Android then I either use Solid Explorer's built-in FTP server or SMB/SSH "share" from the PC.

About the questions of "how is this different from BTSync":

Well, first, and foremost, Syncthing is Open Source Software. You can audit the source code to look for potential security threads (i.e. hidden backdoors, weak crypto). You don't have to rely on promises but you can put it to the test (given you can code and you happen to understand crypto).

Secondly, and most importantly, you can jump into the fun and contribute improvements to the project (fork it, add to it, send a pull request). The biggest advantage of FOSS: You can contribute! If you're just a end-user, well, you can at least provide testing feedback.

Thirdly, Syncthing, in my oppinion, does a good job at maintaining a sane UI, much unlike the trainwreck that is the BTSync 1.4 Beta series.

Seeing how the release at least one new pre-built build a week also shows that they got the idea of "release early, release often" (see "The Bazaar and the Cathedral" to get the idea if you don't know what that means) to not only provide you with updates but also push something out so the masses can give it a shot to try and uncover bugs or test latest improvements.