I've tried to ditch Dropbox for a long time. But the need for synchronizing folders between my computers have held me back. Syncthing solves this for me. It's decentralized syncrhonization between all my units, including my phone, without the need to go through a 3rd party server.
Excerpt from Syncthings homepage: Syncthing replaces proprietary sync and cloud services with something open, trustworthy and decentralized. Your data is your data alone and you deserve to choose where it is stored, if it is shared with some third party and how it's transmitted over the Internet.