Despite various attempts to create something, there isn't really one place. Here are few of the attempts I can think of:
Community Apps (Wiki post on this forum)
Community Device Drivers (FKA Compatible Devices Wiki) (Wiki post on this forum but a conglomeration of community drivers plus devices people have unofficially verified to work with stock/generic drivers)
HubitatCommunity · GitHub (the HubitatCommunity GitHub, really only used by a few projects including the popular HubConnect)
Hubitat Apps (Unofficial ShoutWiki for Hubitat apps and drivers)
- probably more that I'm forgetting--I can add anything to this if anyone points something out
If you have a specific device (or ported app/driver) in mind, the best thing to do is probably a search here on the Community forum to see if someone has created (or ported) something. If you're not sure or can't find anything, there a lot of helpful people here (like ST) and someone will probably comment if they've seen something for it.
PS - While I'm loving the Hubitat Sonos (and unofficial Alexa TTS) integrations a lot, I definitely appreciated LANnouncer on ST and in my early Hubitat days and might find a way to bring it back up again soon, so thanks for that!