You might like Collabora Code. It is a online thin client of libreoffice hosted in a webpage with collaborative editing potential. It should be fine for small g

You might like Collabora Code. It is a online thin client of libreoffice hosted in a webpage with collaborative editing potential. It should be fine for small groups as the main limitation is memory consumption. OnlyOffice looks promising as the design goal is to work with msoffice formats natively. Onlyoffice is client side run so the server could have more Concurrent connections. OnlyOffice has a professional looking companion mobile app. The problem at this time is the challenge of getting either solution to host but at this time there may be services that do that for you. Hosting yourself could give you peace of mind that vital files are strictly in your custody. I have been working on a wizard installer for both with nextcloud but the release is still far off due to my quality concerns.