As I mentioned in my previous post, I've been using Owncloud for several years now. It's been a phenomenal way to control my own data and decouple myself from 3rd party services that change over time. Here's four reasons I use and love Owncloud.
It supports CardDav
This in and of itself would be reason enough to run Owncloud. There are CardDav clients that run on Android, iOS, OS X, Linux, and Windows. Which means you can access your contacts from anywhere, without having to export/import them every time you change your email client or cell phone carrier.
It supports CalDav
Like CardDav, support for CalDav allows you to access your calendar from almost any device. Owncloud also supports shared calendars, which is really useful for families as you can add shared events for everyone to access.
It supports WebDav
I'm going to sound like a broken record, but WebDav support allows you to access your files from almost any device. The web interface allows you to upload and download files even on a shared computer. My wife and I use this all the time to share our photos with each other, family, and friends. We also put all of our music and movies on our server so that we can access it from anywhere.
It has native sync clients
You can install a native app on your mobile devices or desktop and have owncloud sync your files for you automatically. This allows you to not only share your files across all your devices but you now also have an automatic backup of your data. I've benefited from this several times as I've switched phones over the years as well as when I've switched laptops.