After joining several planned DCS missions where a Google spreadsheet was used to share the mission data and for signup, I've had the idea and built a dedicated platform for it.
Please allow me to present https://simmissionplanner.com
The platform lets you create as many squads, campaigns and missions as you like and has many capabilities. A few of them (not limited by) are:
Securing data with passwords
Set squad as private or public.
Add squad members by their callsign and/or let everybody join the squad
Set campaigns and missions to only be visible for squad members or visible for everybody.
Set plane specific data like callsign, task, radio channels and more like adding kneeboard or skin (zip) files for pilots to download and use
Set overall campaign settings which are used when a new mission under that campaign is created. These settings can then be overridden when editing the mission.
More is possible.
The platform is free to use for everybody. I have a passion for DCS and this is my gift to the community.