This APT cheat sheet includes essential commands that you will use everyday in Debian.
This article shows you how to migrate a GPG key and shares useful tips around it.
Packagecloud explains its support for Android AAR in Packagecloud.
Check this article to learn how RubyGem index and metadata work internally.
Check this article to learn how APT repository and metadata work internally.
This article explains Packagecloud's web upload and how you can use it.