BPolite

This app silences the ringer according to events in your calendars. The app is free and it doesn't contain any ads.

General features:
- Silences ringer at the beginning of a meeting and restores the ringer at the end of the meeting.
- Shows a list of calendars that are synced with your device. You can choose to silence the ringer only for events in specific calendars.
- Shows a notification when the ringer is silenced.
- Integration with the excellent app "Shush!". Events that will trigger ringer silencing will not trigger "Shush!" popup.
- Can handle overlapping meetings.

Features that can be configured per calendar:
- Mute or vibrate
- You can add extra minutes to each event in the calendar.
- You can restrict the silencing to take place only on certain days of the week.
- You can restrict the silencing based on meeting availability: free, busy and tentative.

Not supported:
- All day events.
- Calendars that are not synced with your device.

Source code:
https://github.com/yuragr/BPolite