On a first look it seems quite promising.
WebDAV only on mobile and via third-party apps
https://sync-in.com/docs/user-guide/mobile_apps
At the moment, Sync-in does not yet offer a dedicated mobile application. We know this is an important point for many users️ and we plan to address it thanks to community contributions and sponsorship.
NextCloud is a full collaborative platform that includes file-sharing, file-editing, chat, calendars, to-do lists, mail, and more. Does Sync-in provide similar features, or is it only focused on file-sync and collaborative file-editing? Is it really an alternative for NextCloud?
Nextcloud started out as file focused, and many people that run Nextcloud since a while now, consider most of the additional features to be unnecessary bloat; I for example stopped using Nextcloud because of its featuritis and abyssal performance.
