An alternative to Titanpad/PiratePad that I use is Mozilla Etherpad, or sometimes when I'm doing more intense collab with RL friends for other projects (largely visual novels, Python coding, and whatnot), we would use the official, downloadable Etherpad freeware. I'm not a fan of Gdoc, due to it's horrible lag on my computers when there are more than 2 people working on the document at the same time. I also avoid Discord for collab projects because we need a way to be able to keep track and look back past discussion points without having to scroll through slowly to squint for them (I know there's the pin thing, but it's not organized enough).

I might give Trello/Asana a shot. From what I've seen on the official sites, looks quite good.