Are there any Unity Collab alternates?

Hello,
I am wondering whether there are any free Unity Collab alternates for lots of people. We are currently working on a game and we are letting new devs join. They new devs are real game developers, which have made other games with Unity. But there must still be some kind of security, which prevents them for working in specific scenes, codes and files. Are there any alternates or can this also be done in Unity Collab?

Thanks,

 

Pretty sure you can lock files in git, although I have never used this feature so I am unsure. Perforce is paid but also does something similar.