Given that "some kind" of authentication will be necessary, it may be worth having a look at the mobile browser version of google calendar. You would need to set this up in a webviewer
( you could provide buttons to give users the choice, or they can choose as Google throws up an option to go mobile.
Alternately, also avoiding the api (so to speak) you could show a calendar (See calendar settings > Sharing) and use buttons to create events, sending to a google form, which could then populate the calendar, however this could get messy!
All the above might depend on the size of the device for sensible calendar viewing, looks good on a 7 inch tablet!


