What is the best cloud service? - Web-devs

my name is Harrison. I am a web-developer looking for a really simple, easy to use, free alternative to GitHub which i can use with a couple of my colleagues/friends to work on ONE website together. I want it to function like an FTP server but if I do it with an FTP server One person will upload a file to the main branch and override all of the work I have just done! Please provide me with an alternative!!!

Thanks for your co-operation :)