This is a small application to provide three start menu items to change ringer mode between normal, vibrate and silent. Please refer to the screenshot.

I usually do not use this application directly, but use android-init @ https://play.google.com/store/apps/details?id=org.gemini.init to automatically switching between different mode.
A sample is @ https://github.com/Hzj-jie/android-init/blob/master/sample/auto-ringer.sh

This is an open source project. You can find the source code @ https://github.com/Hzj-jie/android-ringer-mode