Our active group just chats in Messenger. Someone sees a raid, posts the time window and tier, and asks for interest (or says they can't make it but saw it). If a nucleus of interested parties forms, the raid happens. When we had scanners, we pretty much did the same thing, except with help from the scanners. The getting people to show up part is the challenge (not a hard one, we usually succeed).
Functioning raid organization?
As people keep complaining that raid scanners are still down, I have to ask: Who else enjoys a system for the organization of raids that is still working? And how?
Our local setup (and I have no idea how they programmed this) uses a map showing only the gym positions. By clicking on the gym symbol, one gets options to submit the type of raid boss or egg, and the runtime of the raid. This automatically creates an interactive post in a Telegram channel. Interested players can use this to indicated, at which time they will be at the gym. If enough players sign up, the raid party will happen.
The time needed to post a raid and to sign up for it is about one minute only. All that is needed are players looking at their game and posting the raids in their vicinity they would be interested in. It is entirely within TOS and not affected at all by the current blackout.
Answers
Discord here, manual scanning, usually a screenshot of the egg with the time left and the name and thumbnail of the Gym disk is enough. We then discuss interest and start times, that's all. We're of course missing movesets from the trackers once it hatches, but when we finally agree to fight it we're enough for any moveset.
That's how we do it to. I post everything I see relavent to my teams area on the way to work with a message that I'm just posting.
It's harder to maximize 1 lucky egg to hit several raids back to back. It also cuts down on the solo ones since I'm not leaving my house randomly to see if a raid that I want to do just happens to be starting for the Pokemon i want.
I've saved a little money. I didn't realize how much I was dropping in this game. That said, this new Kanto event has got me buying balls again. If I wasn't married, I'd just restock at a park that is 20 minutes me that has 8 stops and 4 gyms in less than 3 kilos distance but she is already frustrated that she thinks id rather play the same then spend time with her.
In Singapore, just travel to and wait at places known for exceptionally high gym density and human traffic. There is a small park in Tampines with six gyms, just a five-minute walk from the town centre, which has another six. Those who work in the CBD or Orchard should have no problem finding legendary raids with enough people.
Discord only here; when someone see's a Latios raid, they post it even if they can't do the raid themselves. It's... sort of working? It's not great, but we still tend to get 1 Latios raid organized each night. It's a far cry from the 3-6 we used to be able to do, but it has cut down greatly on the amount of raid passes we need to buy.
So... silver lining?
In a very active raid group via Messenger, which is thanks to a few fanatic members with (it seems) tons of time and money on their hands. Too bad I can only participate with that group during weekends due to my work schedule. Other than just seeing raids when passing by gyms, we also rely on those who are defending the gyms to go check their mons via the "Go to Gym" feature to see if a raid will be happening. Can only tell the level of the raid and start time, though.