Changes have been made in Git (FRAMEWORK_5_1):

commit f0492f96adf4fdd2594409417bcba013d16eeb66
Author: Jan Schneider <jan@horde.org>
Date:   Wed Apr 16 14:57:37 2014 +0200

     Don't pile up modifications in history log.

     The changes introduced for request #10249 did accumulate all event
     modifications in the history log, which eventually lead to bug 
#13113. Until
     Horde_History doesn't scale better for large user numbers, we 
should not log
     even more stuff. Especially if we don't even use this information 
anywhere.

  kronolith/lib/Driver/Sql.php |    4 ++--
  1 files changed, 2 insertions(+), 2 deletions(-)

http://github.com/horde/horde/commit/f0492f96adf4fdd2594409417bcba013d16eeb66

Changes have been made in Git (master):

commit 122e6dfad7a65cb9c9ef59a3eef7e4212e317f9e
Author: Jan Schneider <jan@horde.org>
Date:   Wed Apr 16 14:57:37 2014 +0200

     Don't pile up modifications in history log.

     The changes introduced for request #10249 did accumulate all event
     modifications in the history log, which eventually lead to bug 
#13113. Until
     Horde_History doesn't scale better for large user numbers, we 
should not log
     even more stuff. Especially if we don't even use this information 
anywhere.

  kronolith/lib/Driver/Sql.php |    4 ++--
  1 files changed, 2 insertions(+), 2 deletions(-)

http://github.com/horde/horde/commit/122e6dfad7a65cb9c9ef59a3eef7e4212e317f9e

Changes have been made in Git (master):

commit 0ede15ec4fc473872328fc3d122b9d1837df4039
Author: Jan Schneider <jan@horde.org>
Date:   Wed Apr 16 14:54:39 2014 +0200

     Fix testing for unset old properties.

     Fixes logging all properties that are empty, even if not changed. 
Introduces
     with request #10249.

  kronolith/lib/Driver/Sql.php |    5 +++--
  1 files changed, 3 insertions(+), 2 deletions(-)

http://github.com/horde/horde/commit/0ede15ec4fc473872328fc3d122b9d1837df4039

Changes have been made in Git (master):

commit 4ec07370f94752056bde02ce3958fa8bab6d0d4a
Author: Ralf Lang <lang@b1-systems.de>
Date:   Sat Mar 31 11:40:48 2012 +0200

     Add logging capability for event modify details (Request #10249)

  kronolith/lib/Api.php        |   20 +++++++++-----------
  kronolith/lib/Driver/Sql.php |   37 +++++++++++++++++++++++++++++++++++--
  kronolith/lib/Event.php      |   22 ++++++++++------------
  3 files changed, 54 insertions(+), 25 deletions(-)

http://git.horde.org/horde-git/-/commit/4ec07370f94752056bde02ce3958fa8bab6d0d4a

Changes have been made in Git (develop):

commit 4ec07370f94752056bde02ce3958fa8bab6d0d4a
Author: Ralf Lang <lang@b1-systems.de>
Date:   Sat Mar 31 11:40:48 2012 +0200

     Add logging capability for event modify details (Request #10249)

  kronolith/lib/Api.php        |   20 +++++++++-----------
  kronolith/lib/Driver/Sql.php |   37 +++++++++++++++++++++++++++++++++++--
  kronolith/lib/Event.php      |   22 ++++++++++------------
  3 files changed, 54 insertions(+), 25 deletions(-)

http://git.horde.org/horde-git/-/commit/4ec07370f94752056bde02ce3958fa8bab6d0d4a

No, the Kolab driver writes to the history too.

If I understand the code correctly, history handling happens only in 
the SQL driver but not kolab.

This is already tracked (partially) in Horde_History, though only the 
creation and modification dates at the moment. In the traditional 
interface this information is even displayed already.

It would be cool if users could see in kronolith if they already sent 
out invitations and any edits of the event (who changed what, when).

Is Horde_History a suitable component for that?

I might get at that myself but not before passwd is released.