Calendar Store Brain Dump

January 30th, 2003

Someone just asked me for information on open source calendar stores. This is my brain dump. Might be out of date.

Last time I did a thorough investigation there was no open source, mature, standards compliant calendar server aka calendar store. This is partially because CAP is still in draft after 5 years or so of discussion, and partially because it very complicated protocol.

Lately I’ve been wondering if perhaps Apple and the Mozilla teams will by pass the need for a complex BEEP based Calendar protocol with their examples of how to do calendar sharing with only the iCalendar stanard, and HTTP.

Some options:

  • phpGroupware is probably the most popular of the open source calendar stores. Implements a web calendar, and a dozen other things, and has an API for clients to call into. right now their website is offline however :(
  • MCAL is a library for implementing a calendar store. It is an optional backend to Kronolith, and has some useful abstractions. Development stopped on it a long time ago though, and it doesn’t track the Calsch strandards.
  • libical (aka freeassociation) is a little more challenging to use then MCAL, but is the standard library people use for working with iCalendar objects. (e.g. its used by Evolution)
  • Reefknot is supposed to deliver a full suite of Perl implementations of the Calsch protocols, which would be enough to roll your own CS, unfortunately they got bogged down about a year ago with a long way to go.
  • UW Calendar, from the school that brought you Pine, an iCalendar inspired, Java app. unclear as to the current state of it.
  • The Open Office folks have a groupware initiative that they’ve discussed a lot, don’t know if there is any code.
  • OpenCap was announced with a flourish and some code on the Calsch mailing list, but I don’t think it continued. (I could be slandering them)
  • Interesting email from the original author of libical on a CAP server design

Promising development:

  • Evolution has a lot of momentum, and iCalendar support. They seem one of the most likely groups to put together their own calendar server. Unfortunately they have a commercial product selling compatibility with Exchange, which probably servers as a demotivator.
  • KOrganizer folks have been asking for a server to connect to for a long time, they’ve architected around it. They do have pretty good iTIP support.
  • Kronolith is the web calendar from the Horde project. Has a lot of energy, and active development going on. Support for free/busy queries, and iTIP, working on support iCal over HTTP.
  • Mozilla calendar and Apple calendar both by-pass the need for a Calendar store by publishing over HTTP, Apple with WebDav, and Mozilla with PUT. This is obviously more limited then a full CAP server, but it can work surprisingly well. I’m hoping that this might spark a new wave of calendar innovation.

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