When comparing Business Calendar vs aCalendar, the Slant community recommends Business Calendar for most people. In the question“What are the best calendar apps for Android?” Business Calendar is ranked 6th while aCalendar is ranked 8th. The most important reason people chose Business Calendar is:
Business Calendar offers configurable widgets in many sizes for displaying Days, Weeks, Months or Agenda views on a user's home screen.
Specs
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Pros
Pro Widget support
Business Calendar offers configurable widgets in many sizes for displaying Days, Weeks, Months or Agenda views on a user's home screen.
Pro Free ad supported version available
Business Calendar comes in a free ad supported version.
Pro Smooth zoomable user interface
Business Calendar has a user interface that supports scrolling and pinch zooming.
Pro Search function
Business Calendar has a search function that allows searching the calendar for dates and events.
Pro Integrates with Google Maps
Users who input locations can use Google Maps from an event to find the directions and location.

Pro Move Calendar events from one Calendar to another
The only app that has the ability to move an event to a different calendar if it was accidentally created in the wrong calendar. This app is an essential addition to any device and for anyone with multiple calendar accounts.
Pro Events can be created using the share menu
Pro Can manipulate with multiple events at a time
The app allows selecting multiple events and move or delete them together.
Pro Good Tasks integration
Tasks get shown in the calendar, although there is also a separate tasks view. It supports Google Tasks and recurring tasks.
Pro Very convenient user interaction
Switching from day<->week<->month views by swiping laterally is a powerful feature.
Pro Lots of customization options
The settings menu is rather detailed and includes a good selection of color themes to choose from, possibility to adjust font-size, set beginning and end of day, ability to choose what views to use and more.
Pro Free, ad-less version available
aCalendar is an Android app that comes in free, ad-less version as well as this paid version.
This paid version aCalendar+ adds more features like agenda view, home screen widget and the ability to manage Google Calendars. The developer also donates some of the profits from this Pro version to help protect the endangered mountain tapir.
Pro Nice presentation
The three views are very convenient, particularly the week view, which shows the week position inside the month
Pro Good fullscreen widgets for all views
The app has widgets for day, week and month views.
Pro Color-coding support
The app has 48 calendar and 12 event colors.
Pro Can add public holidays to calendar from over 35 countries
For the 30+ available languages for the app, there are holiday calendars available to be added.
Pro Lunar calendar support
aCalendar can be set up to use a calendar based on cycles of the lunar phases.
Pro Unique Week overview
Its week overview is very well suiting for tasks and all day events. It shows everything at once.
Pro Drag'n'Drop
Drag'n'drop functionality is available in day view with this paid version of the application.
Pro Useful 3-finger tap to go to today
By utilizing a three finger tap shortcut users can easily got to the today view from anywhere in the app.
Pro Available in 30 languages
There are 3o user made translations available for the app, making for a good calendar to use in different countries.
Pro QR and NFC barcode sharing of events
Using both QR codes as well as NFC, users can share events wirelessly and easily
Cons
Con Poor visual design
The design of the app looks a bit dated, something out of the early 2000's. While this does not impede the usefulness of the application, it still is a sore point when compared to some of the other popular calendar apps available on Android.
Con Widgets don't show week numbers correctly on some devices
Widgets on certain devices have been showing week number incorrectly for more than 2 years. The issue hasn't been addressed and there is no sign that it will be.
Examples from S4:
Con Poor support
The developers provide virtually no help with issues.
Con Free version is very limiting
Free version of the application does not include common things like the agenda view, actionable notifications or attendee management among many other more advanced features.
Con Somewhat overwhelming amount of options
