I needed a customizable clock, and had an unused old ebook. This app shows current time, date, battery charge, indoor temperature and prevents lockscreen from being turned on.
For unknown reasons building an app for Android 2.1 in modern Android Studio leads to resource error crash after install, so I had to code it without using xml files. Be aware that an app is meant for 800x600 album layout, so if you want to use your android based ebook as a clock you'll probably have to tweak font size in MainActivity.java. To display temperature I am using the content of /sys/devices/platform/omap3epfb.0/graphics/fb0/epd_temp — location can also depend from your device (if you don't need that, just comment out related lines).
Mikel for his retro android development guide.