The feature to select individual calendars per widget is only on the Pro version. If you read the description on Business Calendar Free, the following text is detailed:
"This is the free version of Business Calendar, it is containing (unintrusive) ads in some views but is fully functional! Even so, the ad-free paid version offers some additional features:
* drag&drop mode in the multi-day view to move and copy events
* option to link a contact to an event
* configurable font sizes for the app and the widgets
* option to select individual calendars for each widget
* own Business Calendar reminders
Please do not move the application to the sd card if you want to use the widgets (general limitation of the Android operating system)!"
Business Calendar Pro is $4.99 on Google Play and was $0.49 for 7 days last week when Google Play celebrated it's inaugural creation. I have been using Business Calendar Pro since last year and I highly recommend it as well! I use Business Calendar Pro's Agenda widget, tracking multiple calendars, and the latest update allowing the user to scroll through the Agenda widget on a third party launcher ( I use ADWLauncher Ex; Also works on Go Launcher, etc.) is a very useful feature that I've always wanted and makes Business Calendar even better as compared to the stock calendar or probably even against other third party calendars.