People lose files to sync tools more often than to hardware failure, and almost always the same way: they used a mirroring tool when they wanted a backup. The mirror did exactly what was asked. You deleted the file on one machine, so it deleted the file on the other, very fast.
Two-way sync keeps machines identical and propagates deletions. One-way mirror makes the destination match the source. Neither is a backup, because a backup keeps history.
At a glance
| Tool | Type | Best for | Licence | Watch out for |
|---|---|---|---|---|
| Syncthing | Two-way sync | Your own machines, no server | MPL-2.0 | No web UI for non-technical users |
| Rclone | Mirror / transfer | Cloud storage, 70+ backends | MIT | 27 advisories in 12 months |
| rsync | Mirror | Scripted Unix mirroring | Not recorded | Unix-native |
| Unison | Two-way sync | Bidirectional with conflict handling | GPL-3.0 | Niche, small community |
| Nextcloud | Server | Teams needing a web UI and sharing | Not recorded | You run a service |
| Seafile | Server | Same, with commercial support | Not recorded | From $100/year |
| ownCloud | Server | Nextcloud's predecessor | Not recorded | Thin data on our side |
| Pydio Cells | Server | Enterprise file sharing | Not recorded | Confidence 0.05 |
| lsyncd | Mirror | Live Linux mirroring | GPL-2.0 | Last release 2022 |
| Resilio Sync | Two-way sync | Peer-to-peer, commercial | Not recorded | Quote-based, no published pricing |
Peer-to-peer sync
Syncthing
MPL-2.0 · free · 88,528 stars · shipped 2026-09-08 · 3 advisories, 0 in the last 12 months (HIGH) · score 56.1, confidence 0.59
Peer-to-peer, so there is no server and no third party holding your files. The best-evidenced entry in this category.
Verdictthe default for syncing your own machines. Free, actively maintained, and nothing leaves your network.
Syncthing alternatives
syncthing alternatives is one of our most-clicked queries, and people arrive for specific reasons rather than because Syncthing is bad.
- You need a web interface for non-technical users then Nextcloud or Seafile.
- You need selective sync from a phone then Resilio Sync, or a server-based option.
- You want one-way mirroring, not sync then rsync or Rclone.
- You need commercial support then Seafile or Resilio Sync.
Nothing here matches Syncthing's combination of free, peer-to-peer and actively maintained.
Unison
GPL-3.0 · 5,474 stars · shipped 2026-05-01 · 0 advisories · score 37.8, confidence 0.59
Bidirectional sync with real conflict handling, which is more than most tools here attempt.
Verdictworth knowing about if conflicts are your actual problem.
Resilio Sync
Quote-based · 4 integrations · score 22.4, confidence 0.75
An unusual combination: we measure it adequately, and what we measure is a product with no published pricing, no public repository and few integrations. That is a genuinely low score rather than a measurement gap.
Verdicthard to recommend without a published price.
Mirroring and transfer
Rclone
MIT · free · 59,745 stars · shipped 2026-09-04 · 29 advisories, 27 in the last 12 months (CRITICAL) · 41 integrations · score 61.6, confidence 0.79
Nothing else here is close on backend coverage, with more than seventy storage providers supported.
That advisory rate is the highest in this category by a wide margin and among the highest we track anywhere. Context matters: a huge surface area, and many advisories come from bundled dependencies rather than Rclone's own code. It is actively maintained.
Verdictstill the right tool for cloud transfers. Keep it updated rather than pinning, and remember it typically holds keys to every cloud account you have configured.
rsync
Free · 5,207 stars · shipped 2026-08-13 · 0 advisories · score 51.4
The oldest answer and still correct for scripted one-way mirroring on Unix.
Verdictuse it. Works on Windows only through a compatibility layer.
lsyncd
GPL-2.0 · 6,063 stars · last release 2022-11-17 · score 29.5
Verdictavoid for anything new. The only genuinely stale entry here.
Self-hosted servers
Nextcloud, Seafile, ownCloud, Pydio Cells
Closer to self-hosted Dropbox than to sync tools, with the operational weight that implies. Seafile publishes from $100/year with a 90-day trial; Nextcloud is open source with a free tier.
Verdictthe answer when a team needs a web interface and sharing. All four are thinly measured on our side (confidence 0.05 to 0.27), so evaluate directly.
Platform notes
Search splits by windows, windows 11, mac, linux. Syncthing, Rclone and Unison run everywhere. rsync and lsyncd are Unix-native, which is the most common reason Windows users end up on Syncthing.
Method, and what we could not verify
Confidence ranges from 0.05 to 0.79. The five entries with no recorded stars or licence are self-hosted server products where our repository signals did not resolve.
We hold no licence record for rsync, Seafile, Nextcloud, ownCloud, Pydio Cells or Resilio Sync. For the open-source ones that is a gap on our side.
Products without a public repository have no advisory data at all, which flatters them in the tables above.
We take no vendor payment for placement.
Evaluate these against your own constraints
Ten tools doing three different jobs. The right one depends on whether you need mirroring, two-way sync or a shared server, and on which operating systems are in play.
Sources
Advisory data from advisories.ecosyste.ms, adoption from GitHub, both retrieved 2026-09-11. Pricing independently observed; each product page links the vendor page it was observed from.