From ACal Wiki
aCal supports CalDAV directly. This is not a hack to stuff events into the Android internal Calendar store, where they don't quite fit, or the format changes from one version to the next: this is a complete CalDAV client which (over time) will expand to support as many features of CalDAV & CardDAV as we can find the time to cover.
aCal supports multiple calendars, hosted on multiple servers. Individual calendars may be marked to display in different colours, set to have alarms ignored, or simply disabled.
aCal will handle display of multiple alarms which may be set relative to the start or end of the event. At present the Event entry screen does not support entry of end-relative events, or arbitrary relative durations, but will honor these if they have been set in a full-featured CalDAV client.
Low Bandwidth & Power Usage
Where possible, aCal uses a recent CalDAV feature called 'WebDAV Synchronisation' to minimise the traffic sent over the wire in it's regular synchronisation activities. You can also configure the sync frequency for each calendar individually, for when the phone is on wireless or on 3g.
While you can't (yet) choose the timezone for an event you create in aCal, an event with a timezone which has been created in a full-function client should be displayed at the correct time in aCal - including triggering the alarms at the correct time.
Easily Readable Screens
aCal is designed to be able to read your events without peering at your phone, and for you to be able to snooze an alarm without having to find your glasses. We've tried to keep the display as simple and uncluttered as possible, while still providing a maximum amount of calendaring functionality.