Your files.
Your machines.

Yes. There is no price, no account and no subscription, and nobody earns anything from it. It is free for personal and non-commercial use under the PolyForm Strict License: you can read the source, but you may not modify or redistribute it, so it is not open source, and using it for a business or at work is not covered. If you want to help, bug reports and improvements are welcome on GitHub.

A dedicated server is optional. A computer you already own can be the hub, or you can run one with Docker. Phones and tablets connect to a hub; they cannot act as one.

Your devices keep complete copies of the folders they chose, so your files are still there. The history lives on the hub, so it is lost with the hub unless you turned on the optional full backup, which is off by default and runs on a desktop or server. A desktop or server device that holds a complete copy of every shared folder can take over as the new hub once you confirm the old one is gone for good; it starts a fresh history, and your other devices reconnect to it.

Sync also carries file deletions between ordinary folder copies. Retained history offers a way back, but keep an independent backup. Arca’s optional full hub backup is off by default and runs on a desktop or server, separately from working copies.

Only you and the devices you pair. Your files travel between your devices and your hub; Arca has no company server in the middle and no telemetry. The desktop app does check GitHub for signed updates, and downloads come from GitHub and Docker Hub. Arca does not claim end-to-end encryption: your hub and paired devices are trusted with your files, and on a local network without HTTPS the traffic is plain HTTP. Open in Maps on a photo opens Google Maps with its location. If you cannot trust your network, use a private network such as Tailscale.

On your hub and on the devices that sync them. Working folders are ordinary files you can open with any app; desktop copies use local paths you choose and phone copies live in app storage. The hub’s history and optional backup are kept in Arca’s own format, so Arca is what reads them. Your own disks set the capacity.

No. Each device chooses whole folders independently, and the folders you sync download as complete files, ready for offline use. A linked phone album adds its photos to a shared folder, and that phone then keeps the complete folder in app storage like any other device.

Only to exchange changes. Once a folder finishes syncing, its local files work offline. Edits wait until the hub is reachable again. An always-on hub makes syncing more convenient.

Yes, if your device can reach the hub. Arca has no public relay, so away from home you need a private network you control, such as Tailscale (a separate service you set up yourself), or your own HTTPS address.

Cloud drives such as Dropbox, iCloud or Google Drive keep your files on a company’s servers. Nextcloud is a full self-hosted platform for many people. Syncthing syncs directly between devices, with no hub. Arca keeps complete copies of the folders each device chooses, and a hub you run keeps the shared folders and their history. It has no accounts or per-person permissions: every device you pair is trusted with all the shared folders, so it suits one person, or a group that trusts each other. It is a different trade-off, not a better one: for per-person sharing, or for no setup at all, those tools may suit you better.

Link a phone album to a hub folder. Arca uploads new photos and videos without recompressing the originals; browse them by date on desktop or the web. Deleting from your phone’s gallery keeps the uploaded files, and hub changes never write back to your Photos library. Deleting a photo in Arca’s shared gallery removes it from every device’s Arca copy, and it stays recoverable while history is kept.

Background work follows iOS and Android scheduling limits. Arca also resumes work when you open it. Keep the app open for a large first upload; background sync is not continuous.

Yes, for as long as the folder’s history keeps it: 30 days by default, adjustable per folder. Restoring needs the hub to be reachable and adds a new version, leaving earlier history intact. Conflicting edits are kept as separate versions for you to review.

The desktop app updates itself from signed releases. Update a Docker server by pulling the new image, and phones by installing the new build. Check the release notes for any requirement to update the hub and its devices together.