I am co-maintainer of the wiki watchlists that are input Fediverse Party. These watchlist have the inclusion criteria that even the intent to build an AP federated app is enough. And if that project is no longer maintained, we’ll keep it on the list still because the code may still be worth a peek by other fediverse developers. Entries are input to the Fediverse Party website itself, that is maintained by one volunteer - @light - who can only spend so much time on it and is aware that for a general audience a different setup is needed.
List maintenance is time-consuming, and a boring chore, but someone has to do it 
Nonetheless the AP apps watchlist is the most complete you’ll find, while the AP dev watchlist created by me is slowly growing. I invite anyone to suggest improvements on the issue tracker, or to become a co-maintainer of the wiki.
As for solutions to manual list aggregation might be using the Murmurations protocol, for which I started two topics:
(These are more focused on documentation; other topics on this forum that go deeper into capability discovery and negotiation a la NodeInfo).
On the whole a serious issue of ‘slow’ Fediverse evolution is that most people are all too happy to work on own projects, but none to willing to spend any time to collaborate across projects and solidify the foundations on which their project stands.
I compared us to Spiral Island, a beautiful though fragile island made with - what other people consider - trash, floating precariously in rough seas of bad tech (the real Spiral Island was destroyed in a hurricane). I’ve been trying to rally others to help build an archipelago, pointing countless people to this community and created Fedi Foundation as a site for community empowerment.
Thus far there hasn’t been much enthusiasm, and I may repurpose the website for my own projects which are on hold because of time spent on advocacy. (I guess I’m finding that “grassroots” means ‘individualism with coincidental encounters along similar interests’). It is what it is… 