# Cachet Drive

> A macOS menu bar app that keeps chosen folders identical across a person's Macs within seconds
> over their own local network, and keeps an encrypted one-way copy in a storage bucket they own.
> It installs no File Provider extension and no kernel extension, so a synchronized folder remains
> an ordinary local folder.

Made by Epiphani Studios. Runs on macOS 15 and later, Apple silicon. Developer ID signed and
notarized.

## What it does, with the mechanism

- Synchronizes folders directly between a person's own Macs using Syncthing (MPL-2.0) as the
  engine, bundled inside the app. Local network only by default: relays and global discovery are
  off unless enabled.
- Leaves the folder as a plain directory on disk. Verifiable: the app registers no File Provider
  domain, which can be checked with `pluginkit -m -p com.apple.fileprovider-nonui`.
- Keeps an encrypted, one-way, versioned copy in the user's own Cloudflare R2 or Amazon S3
  bucket. Credentials live in the macOS Keychain and are passed to the engine in its environment
  at run time, never written to a configuration file and never placed on an argument list.
- Offers two off-site engines, chosen per folder. The standard engine (rclone, MIT) copies whole
  files and keeps a dated copy of anything it replaces. The high-churn engine (Arcamere, ours,
  compiled into the app) uses content-defined chunking and sends only changed blocks.
- Surfaces conflicts rather than resolving them: two edits produce two named files. No code path
  removes a version of a user file without an explicit user action.
- Shows state in the Finder as icon badges and a right-click menu. The extension never talks to
  the engine; the app writes state and the extension reads it.
- Reports its own state without a screen: `--status` and `--status --json`.
- Proves its own logic: `--selftest` runs 47 checks, each decision-shaped check paired with a
  decoy it must fail.

## Measured performance, with conditions

Measured 2026-08-21, MacBook Air 15-inch (M5), two cloud drive clients against 18,001
machine-written files totalling 30.2 GB plus a 21,000-file configuration tree read on every
process start:
- 1-minute load average: 87 with the cloud drive clients, 11 with Cachet Drive.
- fileproviderd processor time: 42% against 0.2%.
- A new file reaching the second Mac: 18 seconds on the same local network, no relay.

Measured 2026-08-22 in a folder of large append-only records. In one day, 179 files changed,
holding 662.5 MB. The comparison below was measured on 59 of those files, holding 260.8 MB, with
the same bytes put through each method:
- Whole-file copy: 260.8 MB sent.
- Content-defined chunking, standard block sizes: 18.9 MB.
- Content-defined chunking, high-churn block sizes: 5.1 MB.
- One file measured on its own: a 3.01 MB record grew by 76 bytes; the engine sent 129,382 bytes
  rather than 3,012,966.

Restores are verified by restoring real files and comparing sha256 against the originals.

## What it runs on and what it is for

Runs on macOS 15 and later. Built for folders that change constantly and are read by software:
source trees, working sets, machine-written logs, journals and transcripts. A cloud drive remains
the right tool for documents a person edits and shares with links, comments and a web view.

## Pricing

$79 USD, one time, per person. Covers every folder and every Mac that person owns, including the
encrypted off-site copy. It is not a subscription and the purchased version keeps working. Priced
per person rather than per machine.

Storage is paid by the user directly to their storage provider, because the bucket is theirs.
Cloudflare R2 lists $0.015 per GB per month with no egress charge (read 2026-08-22).

## Links

- Site: https://cachetdrive.com/
- Capabilities: https://cachetdrive.com/capabilities
- Update feed: https://updates.belstone.com/cachet-drive/