To export your 9flats calendar to other calendars, go to your profile, then go to Hosting, then calendar.
To display your 9flats availability in an external calendar copy this link, or click to download it. Then paste the link, or upload it, into your other calendar.
Example: In you Google calendar: click on "Other calendars, choose "Add by URL" from the drop-down menue and add the link and click "Add calendar". DONE!