To share a calendar with friends, family or coworkers you can use any good cloud service.

For write access usually everyone needs to use the same cloud service, for read-only access this should work across different services.

aCalendar is not involved in sharing, but it is planned to offer setup of sharing for Google calendars directly in the calendar list.

For instructions on how to set up sharing, see the manual of your cloud service, e.g.

Sharing in Google Calendar

Sharing in