It is possible to work with others on the same project in ATLAS.ti (desktop), even if members use different software versions (for Windows or Mac, respectively). You just don't collaborate with each other in real-time and thus have to work with a master project of which you share a copy with other team members. Individually edited copies of the master project must then be merged, creating a new master project. If necessary, you can make copies of this new master project again and distribute them among team members, after which they can be edited again and then merged again, etcetera.
For more information, check:
User Manual chapter Team Work
Video's Teamwork in ATLAS.ti Desktop (Windows/Mac) and How to merge projects in ATLAS.ti Windows.
Please note: handle data (files) with care and be critical when storing and sharing (with each other).
Check out Library Guide Datamanagement, e.g. Storing and sharing research data
Check out How safe are USB sticks? for important insights according USB-sticks.