Many questions are answered simply with add this repository and install.

I understand that Ubuntu developers cannot quickly verify all packages and make them available in official repositories. But is there an unofficial main repository or software center where developers can register their PPAs?

Adding individual repositories is a pain and the update also takes longer as it has to check all the PPAs. Like we have alternative markets for android, it would be great if there are any popular alternative software sources that we can reasonably trust.