Alternative to Overleaf (realtime LaTeX collaboration) With the Ability to have Multiple Collaborators but with no Charge

With many thanks to @LianTzeLim, the solution to my problem is so simple that it is actually contained within Overleaf itself!

Adding collaborators may be behind a paywall, but "link sharing" is still a free service. To collaborate in real-time on your LaTeX document via link sharing, you can do the following:

  1. Have one group member create a project in Overleaf as you normally would.
  2. Click the "Share" Button in the top, right-hand corner of the screen.
  3. Press the "Turn On Link Sharing" link in the box that appears.
  4. Copy the link beneath the box titled "Anyone with this link can edit this project," and share the link with the other members of your group (e.g. via email)
  5. Anyone with that link should be able to edit the LaTeX document, and you should be able to all edit it in real-time!

At present I have not heard any complaints from my students. I will update this if that changes.

source: https://www.overleaf.com/learn/how-to/Sharing_a_project