CalSync Kit, for calendars that live on opposite sides of the IT fence

Field notes

The product uses a scheduled Google Cloud service as the central sync layer, with users connecting calendar providers and defining rules through a private dashboard. Its most specific accommodation is a Power Automate bridge for Microsoft 365 accounts that block ordinary third-party calendar apps, plus a free/busy fallback when that route is unavailable. The page lists Windows, macOS, and Linux deployment scripts, a ten-minute schedule, and a £29 one-time price; the operational claims are presented by the seller rather than independently verified.