DescriptionaCal is a Calendar and Tasklist application which you can use if you have an account on a CalDAV server, such as DAViCal CalDAV Server, or with a CalDAV calendar provider such as dotCal.com, Famjama.com, Yahoo, Google or iCloud, allowing you to share your calendar and todo list across several CalDAV clients, on other phones, or with partners, friends or co-workers.
aCal can also sync from a CardDAV addressbook on the server into your android Contacts (read-only at present).
Calendar clients you could use to access CalDAV calendars on other computers are Apple iCal, Mozilla Lightning, EmClient, Evolution. The iPhone & iPad also natively support CalDAV calendar servers.
aCal is NOT functional as a standalone calendar app: it REQUIRES a CalDAV server connection to work, though it will cope just fine with periods of temporary disconnection.
If you don't want to pay the price to download this pre-built version, the source code for aCal is available on Gitorious and is licensed under the GPL v3, but by donating us this small amount along with your download you will sleep better at night, relaxed in the knowledge that you have helped give us some time to spend on this, rather than being distracted by having to be moneygrubbing capitalists quite so often.
Except for those nights where you set an alarm in aCal to wake yourself up, of course!