I have used an OwnCloud (owncloud.org) server for several years now,
both internally and for a few clients, with great success. It's main
target is file sharing (similar to Dropbox), but it has contacts and
calendaring also which support carddav and caldav.

carddav and caldav are native to OS X (and IOS), and there are clients
available for Android. There is also a fairly decent plugin (addon,
whatever it is called) that does them for Microsoft Outlook.

I mainly use it with our Android phones internally, and with
Thunderbird. Lightning natively supports caldav, but you have to add a
plugin for carddav into the address book.

Tasks are in caldav format, but appear to have some header that shows
them in the task tab under Lightning, and in the task app under Android.

We have separate, shared calendars based on group (Accounting,
Technician, Maintenance, etc...), plus personal calendars which may or
may not be shared depending on the individual users preferences.

NOTE: there is a split from Owncloud called NextCloud (nextcloud.com).
It is my understanding there was a conflict about commercialization, so
the original author created NextCloud as a pure open source project. I
intend to test that and, assuming it does as advertised, move to it, but
I can not say from personal experience how well it works at this time.


Rod

On 05/23/2019 09:44 AM, Hendrik Boom wrote:
> I'm looking for software to handle appointment calendars, contact
> lists, and todo lists.
>
> Yes, I realise I may not find an ideal one. I'm open to wriging my
> own if necessary, or (prefereably) modifying others' open-source
> versions, (or even more prefereably) finding one that is already ideal.
>
> What I'd like it to do, besides the obvious ones of storing my data and
> letting me edit and dispay it.
>
> * I should be able to use it on Devuan.
>
> * Ideally, it should use replicated data. Like the way distributed
> revision control is used to replicate source code. Yes, I'm willing to
> handle merge conflicts manually on sync, but I do want to be in control
> of merging and possible race-conditions.
>
> * I don't want to need aways-on network connectivity,
>
> * I don't want to depend on Google's calendar services, but I'd like to
> be able to use them to coordinate with other people who do.
>
> * I'd like to be able to use established protocols rather than inventing
> my own.
>
> * I'd like to be able to access it on android as well as plain desktop
> Linux. (The desire for android compatibility will drop away if I
> ever get a plain-Linux phone). (This could be a web interface)
>
> * I'd like the system to be simple in concept and execution. No bloat,
> no incomprehensible frameworks, etc.
>
>
> Any ideas?
>
> -- hendrik
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--
Rod Rodolico
Daily Data, Inc.
POB 140465
Dallas TX 75214-0465 US
http://dailydata.net
214.827.2170