Resilio Sync (formerly BitTorrent Sync) by Resilio, Inc. is a
proprietary peer-to-peer file synchronization tool available for
Windows, Mac, Linux, Android, iOS, Windows Phone, Amazon Kindle Fire
and BSD. It can sync files between devices on a local network, or
between remote devices over the Internet via a modified version of
the BitTorrent protocol. 

If you want to run Resilio Sync as a service, you need to have an
rslsync user and group prior to running the service.
Something like this will suffice for most systems:

groupadd -g 364 rslsync
useradd -u 364 -g rslsync -d /dev/null -s /bin/false rslsync

If you want to run rslsync as a regular user, you do not need an
extra system user. You can conveniently start rslsync in user mode
by using the provided rslsync-usermode script.