I run an open source collaboration suite, I'm happy with it, my userbase are happy with it too... all except for calendaring. It's a serious sore point, and I'm scrambling to find a solution.

I've got Courier+Postfix+Maildrop for email, and XMPP/Jabber service all backed on OpenLDAP (corporate directory comes out of LDAP as well). My only sticking point is a half-decent calendaring/scheduling package that has these (seemingly simple) features:

  1. LDAP Integration
  2. Multi-platform support (Windows, Linux and Mac)
  3. Delegation (exec. assistants can manage their exec's calendar, recruiters can schedule meetings in a hiring manager's calendar)
  4. Management of "resources" (meeting rooms, projectors, et cetera)

Nice to haves:

  • web interface
  • the (infamous) Free/Busy
  • Outlook/Palm "conduit" to sync to mobile devices
  • easy administration :)

What I don't want is an entire new collaboration stack (ala Zimbra, OpenXchange, Hula, ...). I like my mail setup, I like my Jabber setup. I just need a calendaring product. I don't expect free (though, that'd be nice), and I'd like some recommendations that someone's actually touched (I'm demanding, I know...) instead of just a list from the CalDav consortium's webpage. ;)

Am I the only one with this problem? Help! :)

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    I like how this question is focused specifically on open source calendaring versus this older question that asks for a full Microsoft Exchange alternative: serverfault.com/questions/5282/… – Philip Durbin May 26 '09 at 20:42
  • Why the aversion to Zimbra? It uses all the common open source email software stack - postfix, spamassassin, openldap, etc. – jtimberman Jun 4 '09 at 7:34
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    I'm against Zimbra because I already have a working mail stack, and in my experience hacking out chucks of a system like that is the start of a disaster that you end up living with for years. – jharley Jun 4 '09 at 21:43
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    At a previous employer (~100 users) we migrated a well established qmail based system over to Zimbra and saved more money than we spent on setup costs (from admin time invested and hardware purchased). Shared calendaring and direct Blackberry support were huge winners, especially for management. YMMV. – jtimberman Jun 5 '09 at 1:04
  • ... I don't disagree that it wasn't a win, but like I said above: I just want a calendaring product. – jharley Jun 5 '09 at 19:29

12 Answers 12


We use Google Calendar in our team, being all linux & mac guys. Otherwise the best common suggestion I've seen is Apple's calendar server:


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  • I have a number of friends in companies who have switched to Google Apps/Google Calendar and it seems to be working reasonably well for all of them. (4 different companies.) – GreenKiwi May 26 '09 at 14:09
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    My company isn't comfortable with sharing such data via a service like Google at this time, so they're off the table (hence the internal IM and Mail services). – jharley May 26 '09 at 17:15
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    The only problem with google apps/calendar is that you're gaining a giant external dependency. They don't have many outages, but they definitely do have outages. – sclarson May 26 '09 at 18:39
  • I second the calendarserver suggestion. While I haven't run it on Linux, it runs extremely well on OSX server and is very full featured. – Kamil Kisiel Jul 16 '09 at 15:20

Check out webcalendar. I think it meets all of your requirements, and all but the mobile option of your nice-to-haves. I haven't used LDAP integration (although it's listed as supported) or delegation, so be sure to check that.

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  • This is looking really promising -- thank you. I'll try to get a copy running in a VM to try it out. – jharley May 27 '09 at 19:44
  • You bet. For us it has been a nice, simple calendar for group calendaring. – pc1oad1etter May 29 '09 at 4:36

We use CalDAV with DAViCal server and Evolution / Kontact on the frontend. Works great. :-)

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Unfortunately, there is a reason why the universe is on MS Exchange.

That said, check out Sun calendar server. I used an ancient version awhile back and it seemed serviceable enough. CalDAV is a quasi-standard, so test, test, test your use cases before writing a check.

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  • Delegation doesn't currently work in the Sun Calendar Server AJAX UI (Convergence) and the previous UI which does support it is ugly as sin. – TRS-80 Jul 2 '09 at 5:53

SOGo might meet your needs.

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I've once set up Mozilla Sunbird on top of WebDAV few years ago so I don't know current status. WebDAV share runs top of Apache so LDAP PAM and SSL is easy to add. It worked pretty well.

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  • webcalenedar works through apache too and sunbird can connect to it – Jure1873 Jul 16 '09 at 14:55

There are a few calDAV packages in Ubuntu, but none of them appear to be heavily used or tested. I think part of the challenge is that many open source companies aren't grown to enterprise scale, and open source development happens in the virtual world of the internet, where you might not need a building and conference rooms.

I think most Ubuntu infra is settling on Google Calendar for the moment; not exactly a shining moment, but suffices for now.

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I would also give a very strong thumbs-up to SOGo. We've got several hundred users at several companies using it and it has proven to be robust and very scalable, with good support from the Inverse team. We use it just about faultlessly with OpenLDAP, Postgresql, Exim and Dovecot. The webmail client is pretty good too.

It integrates into an open-source stack extremely well, and deserves much wider attention.

Windows integration is a sticking point if by Windows integration you mean Outlook. However iCal and Cardav support work well with compliant clients, such as Thunderbird on Windows. However this will hopefully change soon as the SOGo team are experimenting with an OpenChange backend to provide native MAPI support for Outlook. See the OpenChange part of the SOGo overview page for more details.

The calendar and contacts features work extremely on Apple devices, which is very important to management types.

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See also Is there any open source Exchange server?

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  • I don't mean to sound rude, but I specifically mentioned I just want a calendaring product not a whole collaboration suite like Zimbra or OpenXchange or any of those other things... I have a working mail stack, a working directory server and a working IM service already. – jharley May 26 '09 at 20:02
  • Maybe I should have made this a comment instead of an answer, which I just did. Too bad I can't seem to delete this answer, though. – Philip Durbin May 26 '09 at 20:48

You're not the only one, I'm still looking. I'll give you something to stay away from, Bedework. While it looks nice, it lacks delegation and was simply buggy under even a mild load - we ended up with an event that was mostly null and stopped the database backup dump working.

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It's been awhile (6 years) since I've touched this (Now Up-To-Date) product but it was rock-solid then.

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I can't believe nobody has mentioned Zimbra. It has a free (as in beer) and Open Source version that does everything the poster has requested and more. I use it for managing over 50 mailboxes. There are clear instructions for setting it up on an Ubuntu LTS Server here and downloads are available here.

This system uses LDAP, can be run alongside OpenFire for messaging, has group calendaring, documents wiki and heaps of other features.

It also has a multiplatform desktop client (and a web client of course) available for download here.

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