Review of Syncthing powered by the Slant community.
Ranked in these QuestionsQuestion Ranking
Pro Free and open-source
Available for Linux, OS X and Windows and web.
Pro Unofficial Android client available
Pro Works out of the box
Requires no configuration to protect your privacy; it just works.
Pro Reasonably active community forum
Con In beta
Although mostly stable, such stability is not guaranteed, and support is only community driven. Caution advised.