Hopefully there aren't too many hidden, hidden features - but here's some of the less well known and non-intuitive features available for Android that will definitely make your life easier and your apps better.
Your app can fulfill requests from unknown apps to complete actions without needing to know which apps will make the requests. Play this right and you can create the 'default' Twitter app, or booking app, etc.
You can save a lot of battery life using the 返回文章页面重复译者: method to schedule regular events (like server polling or updates). It will synchronize alarms from multiple apps to occur at the same time rather than adhoc.