In the early 2010's, I published some apps on the Google Play Store (https://play.google.com/store/apps/developer?id=Anders+Borlid). Most of them are taken down as of now, due to that I haven't updated any content policies etc. If your are interested, you can download them directly from my Nextcloud server, using this link: https://bit.ly/daftapps
They should still work on any recent Android device, as long as you clicks past the warnings saying that they were written for older Android versions.
One of the apps (JustRoids) was the result of a quite extensive tutorial that is available on this link: http://old.borlid.net/tutorial/
The site is a static snapshot taken from my old Drupal site, so there is no point in trying to login or comment on things.