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Degooglifying (Part IV): Calendar

This post is part of a series in which I am detailing my move away from centralized, proprietary network services. Previous posts in this series: email, feed reader, search.

Finding a replacement for Google Calendar has been one of the most difficult steps so far in my degooglification process, but in the end I’ve found a bunch of great, libre alternatives.

Beyond the basic criteria for free network services, I was looking for:

  • desktop, web and mobile clients
  • offline access, especially for mobile
  • multiple calendars
  • access controls for sharing calendars
  • ability to subscribe and share calendars with other servers
  • applicable for business and personal use

First Attempt: SyncML using SyncEvolution and Funambol

I started with SyncML, an open standard for syncing calendar and contact data. SyncEvolution is a great SyncML client, with both GUI and command line tools available for GNOME and Maemo GNU/Linux, and Funambol is an AGPL SyncML server, with an Android client.

I setup Funambol and migrated from Google Calendar in July 2011, using SyncEvolution on my N900 and my laptop, but there were a bunch of problems. It was unstable around the edges, not handling deletes very well, and sometimes choking and failing with certain characters ( ” maybe?) in event titles. When I tried to switch my parents over in Android, it was a nightmare trying to figure out where the sync was failing, and they eventually moved to Google Calendar instead. SyncEvolution only syncs with Evolution on the desktop; there’s no mature SyncML solution for Lightning. The Funambol free software edition felt like a bit of an afterthought as well, with poor or outdated documentation, and a crippled, totally useless “demo” web UI. There was no calendar sharing or access controls either. Plus, Funambol is a pretty heavy application, targeted at mobile carriers, not someone who wants to run it from their living room.

SyncML with Funambol and SyncEvolution allowed me to leave Google Calendar behind, but I ended up living off my mobile calendar, using Funambol essentially as a backup service. I had no web client, no shared calendars, and eventually stopped syncing to Evolution on my laptop. Part of the problem was Funambol, but part of the problem was also SyncML, which seems to be a clunky standard, designed for an older paradigm of syncing with offline mobile clients.

I quickly realized that CalDAV was the better open standard.

The Solution: CalDAV

CalDAV is an extension of WebDAV, an internet standard for remote access to calendar data. It’s a more modern standard that SyncML — though SyncML does have better support on older mobile devices. (There’s also CardDAV for contacts, but I’ll leave that for a future post.)

Servers: SOGo, ownCloud or Radicale

However, there are a ton of CalDAV servers.

Here are my favourites so far:

Application Pros Cons
Works with anything via connectors; well-integrated with Thunderbird/Lightning, and web UI modelled after Lightning; Ubuntu/Debian repos UI isn’t super pretty; comes with a webmail client I don’t want; heavy, took some effort to install (e.g. made a custom MySQL user auth table, in the absence of an LDAP server)
Very alive; support for contacts, photos, music, etc.; Ubuntu/Debian repos Newer (immature when I first tried in 2011); seemed more of a personal than business tool, but that may have changed.This has changed. As of 2015, ownCloud is strong, mature and thriving.
Radicale Simple, elegant, light-weight For sysadmins: no UI

I tried a few others, but I wouldn’t recommend them:

  • Funambol CalDAV connector: In theory, best of both worlds with SyncML and CalDAV support, but I couldn’t figure out if there was an updated stable version, how to get it working with Funambol, etc., and this would still carry the Funambol issues and lack a web client or CardDAV support
  • DAViCal: seemed robust, but also onerous to configure and administer, and the web UI is only for administration (no web calendar client). This could work, but it just felt a bit onerous to use.
  • Update: lnxwalt mentions PHP Web Calendar, which I’d missed. I tried the online demo, but it looks/feels pretty ~2005: awkward and not fully-featured UI, focus on old standares like iCal (rather than true CalDAV?), with a CVS wishlist that includes SyncML support and a Java servlet, and import/export from Palm as a key feature, etc.

Others I didn’t bother to try:

  • Zimbra: Seemed like heavy-duty Groupware with a bunch of things I didn’t need or want — though could make sense if that’s what you’re looking for.
  • Horde (Kronolith): I did try Horde, but using the old interface a few years back. That UI felt 10+ years old, but it’s since undergone a complete overhaul and I haven’t looked at it since. Also, a groupware suite, which may be a plus or a minus. However, I don’t think it uses real CalDAV
  • Bedework: Java, seems heavy, without any obvious benefits or easy packaging
  • Apple Calendar and Contacts Server: while Apache licensed, it really doesn’t seem to be designed to enable other people to run the software — I didn’t get very far looking into this
  • Update: Jean Baptiste Favre has a great tutorial on implementing SabreDAV, a PHP library which implements WebDAV and its CalDAV and CardDAV extensions, if you want to build your own solution.

I’m using SOGo. Though, that’s partially because it was the most comprehensive solution that I had working at the time when my wife went back to work after maternity leave and we needed sharable calendars again to coordinate scheduling for childcare. But SOGo also has some nice, more advanced features, like the ability to subscribe to remote CalDAV feeds on other servers through the web UI.

I’m pretty happy with SOGo, though I’ll certainly be revisiting ownCloud and Radicale at some point. When I first tried ownCloud, it was immature, but it’s since grown a lot. And when I first tried Radicale, it was using a “strange” ACL model, but that’s been overhauled in 0.8. DAViCal was working, though it wasn’t a pleasure to configure, and I’m sure there are a few other workable servers I passed over.

I highly recommend ownCloud. At the end of 2014, I switched from SOGo to ownCloud, and have not looked back. ownCloud has a better web UI, has a much stronger and vibrant community, is alive and growing, is much easier to host (e.g. repos for popular GNU/Linux distributions, and GLAMP stack), and is useful for more than just CalDAV (I’m already using it for file syncronization and CardDAV as well).

Desktop Client: Lightning

Since I’m a Thunderbird/IceDove user, Lightning is the obvious choice for a desktop client. We also use Thunderbird at the office and in my family. Lightning also supports Google Calendar, so just like with degooglifying email, you can switch your frontend and backend in separate steps.

The Evolution calendar is pretty awkward. I tried it when I was using SyncML, but it didn’t last long. There are other options too.

Web Client: SOGo, ownCloud or CalDavZap

I’d prefer a server with a web client, like SOGo or ownCloud, but for a standalone CalDAV web client (e.g. to pair with Radicale or DAViCal), CalDavZap [demo] seems pretty cool.

Mobile Client: SyncEvolution or aCal

Maemo: The reason I spent so much time on SyncML was that there was no CalDAV client for Maemo, but now SyncEvolution supports CalDAV/CardDAV sync!

Android: Use Davdroid. It syncs CalDAV and CardDAV to native AOSP storage.

aCal is an Android CalDAV client, and a replacement for the proprietary Google calendar application. It works really well, but the UI feels really awkward and non-native. [Update: There’s also CalDAV-Sync, which I’d skipped over because it’s proprietary, but maiki pointed out that the developer at least intends to open source it eventually. I’m not sure if the Android Calendar is free software or one of the proprietary “Google experience” apps?] Both sync to local storage for offline support.


It took me a long time to figure this out, especially since I was focused on SyncML at first, but I’ve finally fully replaced Google Calendar with CalDAV solutions. SOGo, ownCloud and Radicale are all great CalDAV servers. SOGo and ownCloud have built-in web clients, but there’s also CalDavZap as a standalone web client. Lightning is the obvious cross-platform desktop CalDAV client of choice, and SyncEvolution and aCalDavdroid provide mobile clients for Maemo and Android.

The good news is there are plenty of options. As a bonus, most of these come with CardDAV support (which will be the focus of a future post), and ownCloud handles photos, music, and other files as well, so you may get more than just a calendar. Or, if it’s just a calendar you want, light-weight solutions like Radicale and CalDavZap give you just that.

I’m just thrilled to have finally figured this out.

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