Resilio is worth using every day for file synchronization.
Good things: Well made clients for all platforms. Truly decentralized, updating files directly between devices using the same technology as BitTorrent. Free for individuals, commercial versions for enterprises.
Bad things: The source code is closed, meaning it can never be fully trusted. Long term availability and cost may vary due to Resilio's business needs.
Future promise: Well-funded with a plausible revenue stream, so hopefully will be maintained to current high standard.