Overleaf is an Latex tool with chat for simultaneous editing of documents
Overleaf may be free of use for personal use, that is no sharing.
To share with up to 10 collaborator you need a collaborators license and for unlimited number of of participants the professional license will be your choice.
email@example.com administers the licenses aquired by the institute of theoretical astrophysics.
firstname.lastname@example.org orders and handles the orders and payment of the licenses.