When it comes to jotting down ideas, I write them down on some scratch paper so I don't forget them. Then, only after I have jotted all I can, I go to Google Docs to write it up neatly so I have it for whenever.
When it comes to collaborations specific to RP post, I go for Google Docs again. I used to use Titanpad/Piratepad/Etherpad, but that was only because I used to have Windows XP, and that's all it could handle. Now I use Gdocs for just about everything collab and cs-making-related.
As for the actual art of discussion about rps, I either use Skype or Discord. I used to use Chatzy, but like with titanpad and gdocs, I use discord primarily because I don't have a shit computer anymore.
<Snipped quote by The Elvenqueen>
Glad to know I am not the only one that does this!
You can add me to that list.
When I was doing my prep for NaNoWriMo, I jotted down so many ideas on so many sticky notes that my entire desk is full of various sticky notes.