Officially. But there's a huge hacking community around it where you can self host the syncing service. 

https://github.com/reHackable/awesome-reMarkable

TonyGiorgio

[This one?](https://remarkable.com/)

It says

> View, sync, and refine using our apps

And also:

> Access, sync, and store files with cloud storage services

They only list Google Drive, MS OneDrive, and DropBox.

nullama

dtonon

Yup. There's a whole enthusiast community around it with plugins and stuff. 