This application will display a popup window for missed calls, text messages, calendar events and emails via https://f-droid.org/packages/com.fsck.k9. It is extremely customizable with many options to suit your needs and style. Extra themes are available as apks from the website. Anti-feature: Addons. The app has some limitations and the user is prompted to install the fully-featured proprietary version. Status: Newer versions have been published by the author but without source code.