As calmh said, it’s python-syncthing, which talks to the Syncthing API. The other dependencies that may install are requests (HTTP library) and six (Python compatibility library).
Just tried it, apparently the older versions of pip in Debian and Ubuntu repos try to build the wheel causing a bunch of errors if wheel isn’t installed. The install doesn’t seem to actually fail (even though pip doesn’t make it clear that it succeeded). I’ll add a step to upgrade pip in the readme and try building a wheel for the next version to avoid this entirely.