Multiple users editing the same project
You can use Dropbox to share your addons and project files. However you'll want to make sure users “lock” the file before they edit it and unlock it when they are done.
More details open locking and unlocking files using Dropbox can be found here: https://help.dropbox.com/files-folders/share/file-locking
If you do go this route please back-up your project(s). If multiple people edit the same file at the same time, and sync it with Dropbox corrupt your project files.
This is technically a lot harder than using Dropbox, but there are benefits to it.
Again, you’d have to watch out for conflicts. e.g. It wouldn’t be a good idea for multiple people to work on the same project then all try and check back in changes. Again, just make sure only a single person edits and checks back in their project before the next user checks it out and edits it.
This scenario has the benefit of giving you a nice history of changes, and the ability to roll back to a previous version should you need too.