Calandar | free / busy visibility

Hello, I searched quite a bit about that, but could not come to a final clou.

Here's my scenario:
Owncloud is installed on our company's server, several users are using the calendar feature. I'd like to create an overview (e.g. as a separate calendar at owncloud), where I can see calendar entries of my fellow colleagues - without the contents, just the "busy" timeframes. And I'd like to have the possibility to decide which of the personal calendars are integrated into this view: e.g. - the calendar called '"business appointments" is - the cal "public transport schedules" is not.

An optional feature "integrate third party calendars (g**gle, M$ etc) could be nice.

This may already be possible with owncloud - but I never found a HOWTO which makes it easy to handle for me.
NB: I can offer to write such a HOWTO, if I successfully can create a solution.


This feature is not available yet but scheduled for the calendar app version 1.8 (expected end of the year):

What can you do to speed it up? Get your hands dirty and start to code or put some money on it:

Same for the external calendar thingy: