I recently came across Vikunja, and it looks like a great open-source tool that connects Kanban / Agile-style task management with CalDAV.
While exploring it, I noticed that CalDAV sync doesn’t currently work with Thunderbird, which is one of the most popular open-source calendar and email clients (that I use daily). From what I can tell, this has been known for a few years:
Looking at the roadmap, it seems Thunderbird compatibility isn’t currently on the near-term list of priorities. I completely understand that open-source projects need to balance resources and focus, but I’m curious if there’s any background on why Thunderbird integration is particularly tricky.
Maybe understanding the reasons could help others (with more CalDAV experience than me) explore possible contributions or workarounds.
Would love to hear if anyone has more insight or context about the situation.
I’ve tried creating 2 way sync with Nextcloud calendar for example - the biggest bummer is recursive tasks.
Nextcloud is a standalone hosted calendar that has both calendar server and user interface for it, whereas Thunderbird is just a user interface (client).
Nevertheless the problems of integrating Nextcloud with Vikunja are pretty much similar to what it would take to integrate Thunderbird.
(Series Creation) As a user, I want to create a recurring task in Vikunja (e.g., “Weekly Team Standup” every Monday at 9 AM), so that it appears as a correctly repeating event series in my Calendar.
(Series Modification - “This and Following Events”) As a user, I want to change all future occurrences of a recurring event (e.g., move the “Weekly Standup” to 10 AM starting next month), so that both Vikunja and the Calendar reflect this “fork” correctly, preserving the history of past events.
(Single Occurrence Modification - “Exception”) As a user, I want to move a single instance of a recurring event (e.g., next week’s standup is on Tuesday instead of Monday), so that only that specific event is changed in both systems, without affecting the rest of the series.
(Single Occurrence Deletion) As a user, I want to delete a single instance of a recurring event (e.g., cancel this week’s standup because of a holiday), so that it is removed from both systems without deleting the entire series.
(Series Deletion) As a user, I want to delete an entire recurring task series from either Vikunja or the Calendar, so that all occurrences are removed from both systems.
Here I posted my braindump that you could talk through AI for more info on what were my thoughts when designing the solution:
Here’s for example a generous fella created the IOS app that syncs IOS Calendar with Vikunja - similar to what it would take to integrate Thunderbird.
The problem is it most likely lacks all those critical functional requirements I listed above.
Some folks seem to like the solution though and I assume because of it’s relative simplicity it’s going to be not that hard to port this open source app logic as Thunderbird extension (?) given that all Vikunja connecting logic is there and calendar syncing, on the other hand, is standardized for the most part.