With DAVDroid you can sync your contacts, calendars and tasks between Android devices and for example OwnCloud or other self hosted services.
Few days ago a new version of DAVDroid (1.0) was released with some improvements and a complete new desinged interface.
The most important improvement from my point of view is that you can now add and remove ressources from and to an account after it was already set up. With version 0.9.x it was required to remove the complete account and add it again because only when setting up an account you could choose which ressources to add.
The complete relase notes can be found here.
The app is free of charge but you can donate :)