3? I know there is one external project: Isotammi project. Update: see Curated addon collections
Kari (@kku) has some very useful experimentals in his personal repository. But, his do not have lists that the Addon Manager can leverage. You have to install them manually. When they are finished to his satisfaction, they are published in the Isotammi collection.
Eric Doutreleau (GlopGlop @grocanar ) has some of his published to a list for 3 finished addons… but not the experimental ones.
Jean Michault (JMichault @jmichault ) likewise has a list for 5 addons.
I share your frustration with finding and adding addons. (Which is why there is a thread: “What are your favorite plug-ins which have not been distributed?”) But that is hard to find too.
The other frustration is that it is SO hard to share Project configurations for the Addon Manager, scripts for SuperTool, Custom Filters, Dashboard layouts, and similar items.